Monday 2 September 2019

 

09:00-10:30 - Plenary Sessions - Amphi Lavoisier

Chairperson: Carlo Sirtori

09:00 Mo-Pl-1

Passion Extreme Light

Gerard MOUROU, École polytechnique, Palaiseau, France

09:45 Mo-Pl-2

Enlarging the frontiers of research in the IR/mm range using synchotron radiation

Pascale ROY, Synchotron Soleil, France

10:30-11:00 - Coffee Break

11:00-12:30 - Parallel sessions Mo-AM

11:00-12:30 - Mo-AM-1 - Gyrotron 1 - Amphi Lavoisier

Chairperson: Jinjun Feng

11:00 Mo-AM-1-1
THALES TH1507 140 GHz 1 MW CW Gyrotron For W7-X Stellarator
Alberto Leggieri¹; Stefano Alberti²; Konstantinos Avramidis³; Gunter Dammertz³; Volker Erckmann⁴; Gerd Gantenbein³; Jean-Philippe Hogge²; Stefan Illy³; Zisis Ioannidis³; John Jelonnek³; Jianbo Jin³; Heinrich Laqua⁴; Francois Legrand¹; Christophe Lievin¹; Rodolphe Marchesin¹; Ioannis Pagonakis³; Tomasz Rzesnicki³; Philippe Thouvenin¹; Manfred Thumm³; Robert Wolf^4
1Thales Microwave Imaging Sub-systems, France; ²Swiss Plasma Center, École Polytechnique Fédérale de Lausanne, Switzerland; ³IHM - Karlsruhe Institute of Technology, Germany; ⁴Max Planck Institute of Plasma Physics, Germany

The status of the THALES 140 GHz 1 MW CW industrial gyrotron program for the W7-X stellarator is discussed in this paper. The industrial design and performances are briefly discussed with a focus on the tube reliability and endurance. The TH1507 tubes are capable of 1 MW RF CW output power at 140 GHz up to 1800 s. Actually, 9 tubes are running to energize the ECRH of W7-X plant; they can operate with efficiencies up to 44 %. After more than 10 years operation, the 2nd prototype has been opened opened in order to investigate the main physical wear during operation of the tube. This analysis shows an excellent robustness of the tube. It provides a large confidence in the robustness of the future ITER and TCV Thales programs and the upstarting W7-X 1.5 MW tube upgrade

11:30 Mo-AM-1-2
High-efficiency, Long-pulse Operation Of MW-level Dual-frequency Gyrotron, 84/126GHz, For The TCV Tokamak
Stefano Alberti¹; Konstantinos Avramidis²; Andrea Bertinetti³; William Bin⁴; Jeremie Dubray¹; Damien Fasel¹; Saul Garavaglia⁴; Jeremy Genoud¹; Timothy Goodman¹; Jean-Philippe Hogge¹; Pierre-François Isoz¹; Pierre Lavanchy¹; François Legrand⁵; Blaise Marlétaz¹; Jonathan Masur¹; Alessandro Moro⁴; Ioannis Pagonakis²; Miguel Silva¹; Ugo Siravo¹; Matthieu Toussaint^1
1SPC/EPFL, Switzerland; ²IHM, Karlsruhe Institute of Technology, Germany; ³Politecnico Di Torino, Italy; ⁴Institute of Plasma Physics/CNR, Italy; ⁵MIS/Thales, France

The first unit of the dual-frequency gyrotron, 84-126GHz/1MW/2s, for the upgrade of the TCV ECH system has been delivered and is presently being commissioned. During a first phase, long-pulse operation (TRF>0.5s) has been achieved and powers in excess of 0.9MW/0.9s and 1MW/1.2s have been measured in the evacuated RF-load at the two frequencies, 84GHz (TE17,5 mode) and 126GHz (TE26,7 mode), respectively. Considering the different rf losses in the experimental setup, the power level generated in the gyrotron cavity is in excess of 1.1MW and 1.2MW, with a corresponding electronic efficiency of 35% and 36%. These values are in excellent agreement with the design parameters and would likely lead to a gyrotron total efficiency higher than 50% in case of implementation of a depressed collector. The gyrotron behavior is remarkably reliable and robust with the pulse length extension to 2s presently only limited by external auxiliary systems.

11:45 Mo-AM-1-3
DEMO-Relevant Gyrotron Research At KIT
Konstantinos Avramidis¹; Gaetano Aiello¹; Philipp Thomas Bruecker¹; Benjamin Ell¹; Thomas Franke²; Gerd Gantenbein¹; Giovanni Grossetti¹; Stefan Illy¹; Zisis Ioannidis¹; Jianbo Jin¹; Parth Kalaria¹; Alexander Marek¹; Ioannis Pagonakis¹; Sebastian Ruess¹; Tobias Ruess¹; Tomasz Rzesnicki¹; Theo Scherer¹; Martin Schmid¹; Dirk Strauss¹; Manfred Thumm¹; Minh Quang Tran³; Chuanren Wu¹; John Jelonnek^1
1Karlsruhe Institute Of Technology, Germany; ²EUROfusion Consortium, Germany; ³École Polytechnique Fédérale de Lausanne, Switzerland

The DEMO-relevant gyrotron research at Karlsruhe Institute of Technology is driven by the European concept for a demonstration fusion reactor (EU DEMO). This paper reports on the recent results of the theoretical and experimental studies towards the development of gyrotrons fulfilling the DEMO needs.

12:00 Mo-AM-1-4
Powerful Continuous-Wave Sub-Terahertz Large-Orbit Gyrotron
Yuriy Kalynov; Vladimir Manuilov; Aleksander Fiks; Nikolai Zavolsky
Institute of Applied Physics of the Russian Academy of Sciences (IAP RAS), Russian Federation

Coherent subterahertz radiation is achieved for the first time in the large-orbit gyrotron operating at a higher cyclotron harmonic in the continuous-wave generation regime. A stable generation is achieved in the case of operation at the third and the second cyclotron harmonics at frequencies of 0.394 THz and 0.267 THz with a radiation power of 0.37 kW and 0.9 kW, respectively.

12:15 Mo-AM-1-5
Megawatt-Power Dual Frequency Gyrotrons For Modern Fusion Facilities
Leonid Popov¹; Marina Agapova¹; Yury Belov¹; Alexey Chirkov³; Grigory Denisov²; Alexander Gnedenkov¹; Vladimir Ilin¹; Igor Kazansky¹; Ilya Khailov¹; Artem Kuzmin¹; Alexander Litvak²; Vladimir Malygin²; Evgeny Sokolov²; Vladimir Zapevalov²; Vadim Miasnikov¹; Mikhail Morozkin²; Alexander Lyubimov¹; Elena Soluyanova¹; Evgeny Tai¹; Sergey Usachev^1
1GYCOM Ltd, Russian Federation; ²Institute of Applied Physics, Russian Federation

Nearly 20 years ago demand had arisen in the world practice of plasma investigations with gyrotron usage - to have a source of long-pulse microwave radiation with step-tunable frequency at megawatt-power level. Transparency bands of typical modern 1.8-mm single disc diamond output windows are distant at step of ~35GHz. Attempts to build the reliable broad band output window unit capable to provide long-pulse gyrotron multi-frequency operation with much smaller steps has not succeeded yet. In the same time 10 dual-frequency 140/105GHz long-pulse gyrotrons using single disc diamond window successfully run now at megawatt-power level providing ECRH at ASDEX Upgrade and KSTAR facilities.

11:00-12:30 - Mo-AM-2 - Solid State 1 - Petit Amphi

Chairperson: Alexej Pashkin

11:00 Mo-AM-2-1
2D THz Spectroscopic Investigation Of Ballistic Conduction-band Electron Dynamics In InSb
Sarah Houver; Lucas Huber; Elsa Abreu; Matteo Savoini; Steven Johnson
ETH Zurich, Institute for Quantum Electronics, Switzerland

We follow the trajectory of the out-of-equilibrium electron population in low-bandgap semiconductor InSb, using reflective cross-polarized 2D THz time-domain spectroscopy. The 2D THz spectra show a set of distinct features at combinations of the plasma edge and vibration frequencies. We assign these features to electronic nonlinearities, using finite difference time domain simulations, and show that the nonlinear response in the first picoseconds is dominated by coherent ballistic motion of the electrons. We demonstrate that this technique can be used to investigate the landscape of the band curvature near the Γ-point such as anisotropic characteristics in the (100)-plane.

11:30 Mo-AM-2-2
Excitonic Terahertz Emission From Silicon At Steady-State Interband Photoexcitation
Alexey Zakhar'in; Alexander Andrianov
Ioffe Institute, Russian Federation

Converted to poster in the Tuesday Poster Session

11:45 Mo-AM-2-3
Background-free Spectroscopy Of Impurity Transitions In Semiconductors With A Continuous-wave Terahertz Photomixer Source
Martin Wienold¹; Sergey G. Pavlov¹; Nikolay V. Abrosimov²; Heinz-Wilhelm Hübers^1
1German Aerospace Center (DLR), Germany; ²Leibniz-Institut fuer Kristallzuechtung, Germany

We present a method for background-free spectroscopy of shallow impurity transitions in semiconductors with residual impurity concentrations. The method is based on a continuous wave terahertz photomixer source and a scheme for optically modulating the concentration of neutral impurities.

12:00 Mo-AM-2-4
Tunable Stokes Shift In Uniaxially Stressed Silicon With Shallow Donors
Roman Zhukavin¹; Sergey Pavlov²; Andreas Pohl³; Nikolay Abrosimov⁴; Helge Riemann⁴; Britta Redlich⁵; Heinz-Wilhelm Hübers²; Valery Shastin^1
1Institute for Physics of Microstructures, Russian Federation; ²Institute of Optical Sensor Systems, German Aerospace Center (DLR), Germany; ³Department of Physics, Humboldt-Universität zu Berlin, Germany; ⁴Leibniz-Institut für Kristallzüchtung, Germany; ⁵Radboud University Nijmegen, Institute for Molecules and Materials, FELIX Laboratory, Netherlands

Experimental investigations of THz emission from silicon (Si) doped by shallow donors under uniaxial stress along the [001] crystal axis upon selective intracenter excitation by an infrared free electron laser are presented. spectral dependences of Si output integral emission on the pump wavelength and Si laser output terahertz emission spectra have been analyzed. Two mechanisms of stimulated emission have been recognized as inversion-population-based lasing and stimulated Raman scattering. It is shown that uniaxial stress allows to control the Stokes shift and by this the output Raman emission frequency in the active medium. The obtained results demonstrate the feasibility of broad range THz tuning in doped silicon by means of uniaxial stress.

11:00-12:30 - Mo-AM-3 - Metrology - Room 269

Chairperson: François Simoens

11:00 Mo-AM-3-1
Metrology Of Complex Refractive Index For Solids In The Terahertz Regime Using Frequency Domain Spectroscopy
Steven Chick¹; Guy Matmon²; Ben Murdin¹; Mira Naftaly^3
1University of Surrey, Advanced Technology Institute, United Kingdom; ²Paul Scherrer Institute, Laboratory for Micro- and Nanotechnology, Switzerland; ³National Physical Laboratory, United Kingdom

We present a metrological study of a new technique for measuring the complex refractive indices of solids in the THz regime. The technique is widely applicable thanks to requiring only frequency-domain spectroscopy, and is shown to be capable of high accuracy reconstruction of the complex refractive index (RI) spectrum. We quantify the sensitivity to experimental imperfections such as noise, showing that the new technique is more robust than previous methods. We demonstrate the extraction of RI of crystalline Si between 2 -- 20 THz using this method, and comment on the capability to discriminate between absorption and scattering using only a power-transmission measurement.

11:30 Mo-AM-3-2
Comparison Of Waveguide And Free-Space Power Measurement In The Millimeter-Wave Range
Andreas Steiger; Mathias Kehrt; Rolf Judaschke
PTB, Germany

A comparison of waveguide-based and free-space power measurements was carried out in the millimeter-wave range at PTB. The measurements revealed good agreement at 100 GHz of both power scales within their uncertainties. This confirms the consistent realization of SI traceable electronic and photonic power measurements at the national metrology institute of Germany.

11:45 Mo-AM-3-3
Average-Power-Scaling Of Broadband THz Radiation To 50mW
Joachim Buldt; Michael Mueller; Henning Stark; Cesar Jauregui; Jens Limpert
Institute of Applied Physics, Germany

We present on power scaling of broadband THz radiation. By using the two-color gas plasma scheme driven by a state-of-the art, ultrafast, high-average-power fiber laser system an unprecedented to average power of 50 mW. The possibilities for further scaling are discussed.

12:00 Mo-AM-3-4
Nicolson-Ross-Weir Method Using 1-port Network Analyzer For MmW And THz Material Characterization
Seckin Sahin; Niru Nahar; Kubilay Sertel
The Ohio State University, ElectroScience Laboratory, United States

We present a simplified Nicolson-Ross-Weir (NRW) material characterization procedure that employs only a 1-port network analyzer for data collection. This approach is particularly attractive for mmW and THz applications, as it eliminates the need for costlier 2-port measurements which are required in the conventional NRW method. Using two successive calibrations of the measurement port, we calculate the 2-port response of the sample under test. We demonstrate our approach for the WR8.0 waveguide band using a multi-offset-short calibration method. The particular calibration also provides frequency regions of validity as a byproduct of the procedure. Subsequently, the conventional NRW analytic procedure is applied to extract material permittivity and permeability using 2 successive 1-port measurements.

12:15 Mo-AM-3-5
Terahertz Continuous Wave System For Measuring Sub-100-µ M-thick Samples Using Gouy Phase Shift Interferometry
Dahye Choi; Il-Min Lee; Kiwon Moon; Dong Woo Park; Kyung Hyun Park
Electronics and Telecommunications Research Institute (ETRI), Republic of Korea

Terahertz continuous wave (CW) system for measuring sub-100-µm-thick samples using Gouy phase shift interferometry is proposed and demonstrated. When the optical path difference (OPD) of the interferometer is zero, destructive interference pattern is produced. In this case, OPD change induced interference signal change is sensitively detected and can be predicted with calculation. By minimizing the difference between the measured and the calculated signal, thickness of a sample can be determined. Thicknesses of sub-100-?m-thick samples are determined with the 5 % accuracy at 625 GHz.

11:00 -12:30 - Mo-AM-4 - THz Detectors 1 - Room 162

Chairperson: Kaz Hirakawa

11:00 Mo-AM-4-1
A Photomultiplier Tube With Sensitivity In The Entire Terahertz- And Infrared Frequency Range
Simon Lehnskov Lange¹; Naoya Kawai²; Peter Uhd Jepsen^1
1Technical University of Denmark, Denmark; ²Hamamatsu Photonics K.K., Electron Tube Division, Toyooka factory, Japan

We present here for the first time a photomultiplier tube (PMT), which is sensitive to light in the entire terahertz (THz)- and infrared frequency range. The PMT consists of a meta-material-based photocathode and a dynode electron multiplier system kept under vacuum. The photocathode principle is based on ultrafast electron cold field emission (CFE). This principle makes the PMT sensitive to the electric field of the incident radiation. The PMT therefore gives direct access to a host of characteristics of the incident radiation such as polarization, absolute polarity and absolute peak electric field strength with few-ns time resolution.

11:30 Mo-AM-4-2
Plasmonic Nanocavities For High-Responsivity And Broadband Terahertz Detection
Nezih Yardimci; Deniz Turan; Semih Cakmakyapan; Mona Jarrahi
University of California - Los Angeles, United States

We present a high-responsivity and broadband photoconductive terahertz detector based on a plasmonic nanocavity, which enables high quantum efficiency and ultrafast operation without using short-carrier-lifetime substrates. We experimentally demonstrate that a terahertz time-domain spectroscopy setup employing the presented detector can offer 102 dB dynamic range over 0.1-4.5 THz.

11:45 Mo-AM-4-3
Efficient Terahertz Detection With Perfectly-Absorbing Metasurface
Lucy Hale¹; Tom Siday¹; Polina Vabishchevich²; Charles Harris²; Ting Luk²; John Reno²; Igal Brener²; Oleg Mitrofanov^1
1University College London, United Kingdom; ²Sandia National Laboratories, United States

We demonstrate a unique photoconductive design for terahertz (THz) detection based on a perfectly absorbing, all-dielectric metasurface. Our design exploits Mie resonances in electrically connected cubic resonators fabricated in low-temperature grown (LT) GaAs. Experimentally, the detector achieves very high contrast between ON/OFF conductivity states (10^7) whilst also requiring extremely low optical power for optimal operation (100 μW). We find that the Mie resonances dissipate sufficiently fast and maintain the detection bandwidth up to 3 THz.

12:00 Mo-AM-4-4
Grating-assisted Electro-optic Sampling For Enhanced THz Detection Efficiency.
Alexei Halpin¹; Wei Cui¹; Aidan W. Schiff-Kearn¹; Kashif Masud Awan²; Ksenia Dolgaleva³; Jean-Michel Menard^1
1University of Ottawa, Department of Physics, Canada; ²Stewart Blusson Quantum Matter Institute, University of British Columbia, Canada; ³University of Ottawa, University of Ottawa, School of Electrical Engineering and Computer Scie, Canada

The use of nonlinear crystals for detection of THz radiation using electro-optic sampling (EOS) is widespread. Phase-matching typically restricts the bandwidth and detection efficiency for EOS. Here we exploit nanofabrication techniques to etch phase-masks into a <110>-cut GaP crystal, to allow for phase-matched detection THz detection. Our method allows to nearly double the detection bandwidth for the chosen crystal thickness, while also increasing the EOS detection efficiency by approximately 40%. Our method can be easily extended to other nonlinear media, or more complex photonic structures, and is highly applicable for broadband high-sensitivity spectroscopy.

12:15 Mo-AM-4-5
Detection Of THz-waves Using The Photomixing Approach
Florin Lucian Constantin
Laboratoire PhLAM, CNRS UMR 8523, France

The quadratic response to the optical fields and the nonlinear electrical response of a LTG-GaAs photomixer are exploited for detection of THz-waves. The rectification and the heterodyne detection in the THz regime using the photomixing approach are theoretically and experimentally demonstrated.

12:30 Mo-AM-4-6
Development Of Multistage Terahertz Wave Parametric Detector
Hikaru Sakai; Kosuke Murate; Yunzhuo Guo; Kodo Kawase
Nagoya University, Japan

The quadratic response to the optical fields and the nonlinear electrical response of a LTG-GaAs photomixer are exploited for detection of THz-waves. The rectification and the heterodyne detection in the THz regime using the photomixing approach are theoretically and experimentally demonstrated.

11:00-12:30 - Mo-AM-5 - THz TDS 1 - Room 151

Chairperson: Guilhem Gallot

11:00 Mo-AM-5-1
Time-Domain Detection Of The Electric Field And Its Conjugate Variable In Ultrabroadband Electro-Optic Sampling
Philipp Sulzer; Kenichi Oguchi; Jeldrik Huster; Andreas Liehl; Cornelius Beckh; Alfred Leitenstorfer
University of Konstanz, Germany

We demonstrate unambiguous detection of the conjugate variable to the electric field in a time-domain experiment. The polarization change induced by nonlinear mixing of probe and multi-THz fields via the Pockels effect is examined concerning changes in ellipticity and tilting of the polarization ellipsoid. Spectrally resolved measurements yield crucial insights into how sum and difference frequency generation processes shape the electro-optic signal for different detection crystals. This approach enables precise, even simultaneous, measurement of the electric field and its conjugate variable by combinations of different phase biases (lambda/4 and lambda/2) and spectral filtering.

11:30 Mo-AM-5-2
SLD-driven Terahertz Cross-correlation Spectroscopy
Daniel Molter¹; Michael Kolano¹; Georg von Freymann^2
1Fraunhofer ITWM, Germany; ²Department of Physics and Research Center OPTIMAS, University of Kaiserslautern, Germany

Terahertz cross-correlation spectroscopy is a fascinating method to generate signals comparable to those of conventional time-domain spectroscopy but using continuous light. We demonstrate the use of a superluminescent diode to drive a cross-correlation spectroscopy system resulting in a truly continuous terahertz spectrum.

11:45 Mo-AM-5-3
Single-shot Detection Of Terahertz Waveforms Using Non-collinear Time-encoding Technique
Kenichi Izumi¹; Kohei Kawana¹; Masataka Kobayashi¹; Yusuke Arashida²; Jun Takeda¹; Ikufumi Katayama^1
1Yokohama National University, Yokohama National University, Japan; ²Tsukuba University, Japan

We have developed a new scheme for accurately measuring terahertz (THz) waveforms based on a single-shot method using non-collinear time-encoding technique. In this scheme, THz pulses were focused non-collinearly on a LiNbO3 plate with a Si prism coupler together with chirped sampling pulses, enabling us to spatially separate sum- and difference-frequency components from the detected signals. This new approach -- single-sideband detection of each component -- reduces the waveform distortion, and then improves the temporal resolution of the time-encoding technique.

12:00 Mo-AM-5-4
Jones Matrix Calibration And Determination Of The Precision Of Terahertz Time-domain Polarimetry Based On Spinning E-O Sampling Technique
Kuangyi Xu¹; M. Hassan Arbab^2
1Stony Brook University, United States; ²Stony Brook University, United States

We have developed a terahertz polarimetry system by applying frequency modulation to electro-optic detection. A hollow-shaft motor rotates the detector crystal and the modulated signal is read by a lock-in-type reading instrument. We characterize the precision of this system to be approximately 1.3 degrees. Furthermore, we calculate the Jones matrix of the optical components to calibrate the systematic error induced by them.

12:15 Mo-AM-5-5
Time-Resolved Optical Pump -THz Ellipsometer Probe Measurements
Bong Joo Kang¹; Gregory Gäumann¹; Premysl Marsik²; Christian Bernhard²; Thomas Feurer^1
1University of Bern, Switzerland; ²University of Fribourg, Switzerland

We present the first optical pump-THz ellipsometer probe setup together with proof of principle measurements carried out on an UHR-silicon wafer. The retrieved time-resolved dielectric properties of NIR-pumped silicon show good agreement with two temperature model simulations.

11:00-12:30 - Mo-AM-6 - QCL 1 - Room 101

Chairperson: Karl Unterrainer

11:00 Mo-AM-6-1
Sub-terahertz Quantum-cascade Laser Source Based On Difference-frequency Generation
Kazuue Fujita; Shohei Hayashi; Akio Ito; Masahiro Hitaka; Tatsuo Dougakiuchi; Tadataka Edamura
Hamamatsu Photonics K.K., Japan

Authors report a sub-terahertz monolithic semiconductor source based on a high power, long-wavelength quantum cascade laser. In order to obtain higher nonlinear susceptibility in the sub-terahertz frequency region, we design long wavelength dual-upper-state active region in which transition dipole moments are substantially increased. A fabricated device with distributed feedback grating produces nearly watt-level infrared output power, and as a result, it exhibits a peak output power of ~20 ÃZ¼W at room temperature, around a frequency of ~700 GHz. Besides, the device produces an output power of 103 ÃZ¼W at 110 K.

11:30 Mo-AM-6-2
High-quality N-type Ge/SiGe Multilayers For THz Quantum Cascade Laser
Monica De Seta¹; Michele Montanari¹; Chiara Ciano¹; Luca Persichetti¹; Luciana Di Gaspare¹; Michele Virgilio²; Giovanni Capellini³; Marvin Zoellner³; Oliver Skibitzki³; David Stark⁴; Giacomo Scalari⁴; Jerome Faist⁴; Douglas Paul⁵; Thomas Grange⁶; Stefan Birner⁶; Mario Scuderi⁷; Giuseppe Nicotra⁷; Oussama Moutanabbir⁸; Samik Mukherjee⁸; Leonetta Baldassarre⁹; Michele Ortolani^9
1Università Roma Tre Dipartimento di Scienze, Italy; ²Dipartimento di Fisica "E. Fermi", Università di Pisa, Italy; ³IHP-Leibniz-Instut für innovative Mikroelektronik, Germany; ⁴Institute for Quantum Electronics, ETH Zürich, Switzerland; ⁵School of Engineering, University of Glasgow, United Kingdom; ⁶nextnano GmbH, Germany; ⁷Istituto per la Microelettronica e Microsistemi (CNR-IMM), Italy; ⁸École Polytechnique de Montréal, Department of Engineering Physics, Canada; ⁹Dipartimento di Fisica Università La Sapienza, Dipartimento di Fisica, Italy

We investigate optical and structural properties of n-type Ge/SiGe coupled quantum well systems, to assess the growth capability with respect to QCL design requirements, carefully identified by means of a modelling based on the non-equilibrium Green function formalism.

11:45 Mo-AM-6-3
1.65 THz Spanning Homogeneous THz Quantum Cascade Laser: Comb Operation And Injection Locking
Andres Forrer; David Stark; Martin Franckié; Tudor Olariu; Mattias Beck; Jérôme Faist; Giacomo Scalari
ETH Zürich, Switzerland

A homogeneous THz Quantum Cascade Laser with emission spectra spanning over 1.65 THz in a bi-stable, voltage driven regime is presented. A nearly 1 THz emission spectrum in the stable regime showing a narrow electrical beatnote indicating frequency comb operation is observed. Such a narrow beatnote could then be injection locked to an external RF source with powers low as -55 dBm. Together with the low threshold current density of 115 A/cm-2 this design could lead to octave spanning THz QCL frequency combs.

12:00 Mo-AM-6-4
Si-based N-type THz Quantum Cascade Emitter
David Stark¹; Luca Persichetti²; Michele Montanari³; Chiara Ciano³; Luciana Di Gaspare²; Monica De Seta²; Marvin Zöllner⁴; Oliver Skibitzki⁴; Giovanni Capellini⁴; Michele Ortolani⁵; Leonetta Baldassarre⁶; Michele Virgilio⁷; Thomas Grange⁸; Stefan Birner⁸; Kirsty Rew⁹; Douglas Paul⁹; Jérôme Faist¹⁰; Giacomo Scalari^10
1ETH Zurich, Switzerland; ²Università di Roma Tre, Italy; ³Università di Roma Tre, Italy; ⁴IHP-Leibniz-Institut für innovative Mikroelektronik, Germany; ⁵Università di Roma "La Sapienza", Italy; ⁶Università di Roma "La Sapienza", Italy; ⁷Università di Pisa,, Italy; ⁸nextnano, Germany; ⁹University of Glasgow, United Kingdom; ¹⁰ETH Zurich, Switzerland

Employing electronic transitions in the conduction band of semiconductor heterostructures paves a way to integrate a light source into silicon-based technology. To date all electroluminescence demonstrations of Si-based heterostructures have been p-type using hole-hole transitions. In the pathway of realizing an n-type Ge/SiGe terahertz quantum cascade laser, we present electroluminescence measurements of quantum cascade structures with top diffraction gratings. The devices for surface emission have been fabricated out of a 4-well quantum cascade laser design with 30 periods. An optical signal was observed with a maximum between 8-9 meV and full width at half maximum of roughly 4 meV.

12:15 Mo-AM-2-6-5
Stabilizing A Terahertz Quantum-cascade Laser Using Near-infrared Optical Excitation
Tasmim Alam¹; Martin Wienold¹; Xiang Lü²; Lutz Schrottke²; Holger T. Grahn²; Heinz-Wilhelm Hübers^1
1German Aerospace Center (DLR), Germany; ²Paul-Drude-Institut für Festkörperelektronik, Germany

We demonstrate a technique to simultaneously stabilize the frequency and output power of a terahertz quantumcascade laser. The technique exploits frequency and power variations upon near-infrared excitation and does not require an external terahertz optical modulator. By locking the frequency to a molecular absorption line, we obtain a linewidth of about 260 kHz and root-mean-square power fluctuations as low as 0.03%.

11:00-12:30 - Mo-AM-7 - Gas Spectro. & Sensing 1 - Room 201

Chairperson: Olivier Pirali

09:00 Mo-AM-7-1
High-Precision Mid-Infrared Spectroscopy With A Widely Tuneable SI-Traceable Frequency-Comb-Stabilised QCL
Dang Bao An Tran¹; Rosa Santagata¹; Mathieu Manceau¹; Anne Cournol¹; Louis Lecordier¹; Berengere Argence¹; Olivier Lopez¹; Sean K Tokunaga¹; Fabrice Wiotte¹; Haniffe Mouhamad¹; Andrei Goncharov¹; Michel Abgrall²; Yann Le Coq²; Hector Alvarez-Martinez²; Rodolphe Le Targat²; Won Kiu Lee²; Dan Xu²; Paul-Eric Pottie²; Anne Amy-Klein¹; Benoit Darquie^1
1Laboratoire de Physique des Lasers, CNRS-Université Paris 13, France; ²LNE-SYRTE, Observatoire de Paris, Université PSL, CNRS, Sorbonne Université, France

We report measurements of absolute frequencies of various polyatomic species around 10 µm, at level of accuracies ranging from 10 Hz to 10 kHz, using a widely tuneable SI-traceable optical frequency comb-stabilized quantum cascade laser.

11:30 Mo-AM-7-2
Gas Spectroscopy At 222 -- 270 GHz Based On SiGe BiCMOS Using A Multi-Pass Ring Cell
Nick Rothbart¹; Klaus Schmalz²; Heinz-Wilhelm Hübers^1
1German Aerospace Center (DLR), Germany; ²IHP - Leibniz-Institut für innovative Mikroelektronik, Germany

We present broadband gas spectroscopy based on SiGe BiCMOS technology. A bandwidth of about 222 -270 GHz is achieved by a combination of two frequency bands on single transmitter and receiver chips. The antennas of transmitter and receiver for both bands are closely placed on a single chip such that coupling into the same optical system can be realized. We coupled the beams into a compact custom-made multi-pass ring cell with an optical path length of 1.9 m. We demonstrate sensitive gas spectroscopy capabilities by a full bandwidth spectrum of methanol.

11:45 Mo-AM-7-3
Tabletop Terahertz Chemical Sensor For Breath Analysis And Analytical Gas Sensing
Ivan Medvedev¹; Daniel Tyree¹; Parker Huntington¹; Jennifer Holt²; Ajani Ross¹; Robert Schueler¹; Christopher Neese²; Douglas Petkie^3
1Wright State University, Department of Physics, United States; ²The Ohio State University, Department of Physics, United States; ³Worcester Polytechnic Institute, Department of Physics, United States

We report on the design and development of a tabletop THz chemicals sensor capable of detecting a wide range of volatile organic compounds with absolute specificity at a part per trillion (ppt) level of dilution. The system is capable of rapid detection of light volatile compounds and was designed for quantitative analytical gas chemical sensing with specific focus on diagnostic breath sensing

12:00 Mo-AM-7-4
An Integrated Photoacoustic Terahertz Gas Sensor
Mattias Verstuyft¹; Elias Akiki²; Benjamin Walter³; Marc Faucher²; Mathias Vanwolleghem²; Bart Kuyken^1
1Ghent University, Belgium; ²IEMN Lille, France; ³Vmicro, Belgium

An on-chip transducer of terahertz light, absorbed by a trace gas, to a mechanical motion using photoacoustics is proposed. The silicon chip confines light in an optical cavity, wherein an acousto-mechanical cavity is housed. The concentration of a trace gas can be determined from the amplitude of a membrane's motion. The simulations presented here predict a minimum detectable limit of 1 ppm of methanol for 1 mW of terahertz power.

12:15 Mo-AM-7-5
Broadband Terahertz Heterodyne Spectrometer Exploiting Synchrotron Radiation At Sub-megahertz Resolution
Gaël Mouret¹; Joan Turut²; Zachari Buchanan³; Olivier Pirali⁴; Marie Aline Martin-Drumel⁴; Pacale Roy⁵; Francis Hindle¹; Sophie Eliet-Barois²; Jean François Lampin^2
1Université du Littoral Côte d'Opale, France; ²Institut d'Electronique Microélectronique et Nanotechnologie (IEMN), CNRS, France; ³Department of Chemistry, University of California, United States; ⁴Institut des Sciences Moléculaires d'Orsay, CNRS, Univ. Paris-Sud, Université Paris-Saclay, France; ⁵SOLEIL synchrotron, France

A new spectrometer on the AILES beamline of the SOLEIL synchrotron facility to achieve sub-MHz resolution in the THz and far-IR regions is currently being developed. Thanks to a dedicated heterodyne detection by use of a new kind of molecular laser as local oscillator along with a Fast Fourier Transform Spectrometer, several pure rotation absorption lines of H2S and CH3OH around 1.073 THz have been recorded.

12:30-14:00 - Lunch

14:00-16:00 -  Parallel sessions Mo-PM1

14:00-16:00 - Mo-PM1-1 - Gyrotron 2 - Amphi Lavoisier

Chairperson: Stefano Alberti

14:00 Mo-PM1-1-1
Dynamics Of Multimode Gyrotron Locked By Quasi-Monochromatic External Signal
Yulia Novozhilova; Gregory Denisov; Vladimir Bakunin
Institute of Applied Physics RAS, Russian Federation

Oscillation regimes in a multimode gyrotron under the influence of quasi-monochromatic external signal with a frequency close to the operating mode frequency are studied. The calculations were performed for a powerful 170 GHz gyrotron developed at IAP RAS as a perspective prototype for ITER. The parameter regions were found where the frequency of operating mode is locked by external signal and follows the variations in the external signal frequency.

14:30 Mo-PM1-1-2
1.2 THz Second Harmonic Gyrotron With Selective Groove
Ilya Bandurkin; Alexey Fedotov; Andrey Fokin; Mikhail Glyavin; Alexey Luchinin; Ivan Osharin; Andrey Savilov
Institute of Applied Physics of the Russian Academy of Sciences (IAP RAS), Russian Federation

A method of selective discrimination of spurious low-harmonic oscillations in gyrotron operating at a high cyclotron harmonic was experimentally demonstrated in a 1.2 THz second cyclotron harmonic tube at a very high transverse mode TE 58,13. The obtained results prove the feasibility and efficiency of the proposed method of mode selection in the THz frequency range, and may be used in the design of a THz CW gyrotron operating at the third cyclotron harmonic.

14:45 Mo-PM1-1-3
High Power Millimeter Waves Generated By An Overmoded Relativistic Cherenkov-type Oscillator
Jinchuan JU; Juntao HE; Xingjun GE; Junpu LING; Ting SHU
National University of Defense Technology, China

An overmoded relativistic Cherenkov-type high power millimeter wave generator operating in Ka-band has been investigated. The associated particle-in-cell (PIC) simulation and experimental results are presented in this paper. The relativistic electron beam with a peak current of 9.9 kA was generated by a pulsed power accelerator launched at a voltage of 605 kV. The relativistic electron beam was guided by an axial magnetic field of about 1 T and transported through the overmoded slow-wave structure. Typically in experiments, the millimeter wave power radiated in the far field was about 630 MW with a frequency of 32.1 GHz and a pulse width of about 10 ns. The radiation mode was well controlled to be quasi-TM01 mode.

15:00 Mo-PM1-1-4
Long-pulse High-efficiency Relativistic Cherenkov Oscillators At L- And S- Bands
Xingjun GE
College of Advanced Interdisciplinary Studies, National University of Defense Technology, China

This paper presents the mechanism and realization of the long-pulse high-efficiency relativistic Cherenkov oscillators operating at L- and S-bands. In simulation, microwaves centred at 1.53 GHz are generated, with power of 2.4 GW, and efficiency of 38%. By optimizing the scheme of electron beam collection, the phenomenon of pulse shortening is effectively suppressed. In the experiment, microwaves centred at 1.52 GHz are generated, with power of 2 GW, efficiency of 33% and pulse duration above 140 ns. Furthermore, an S-band relativistic Cherenkov oscillator is designed. In simulation, microwaves centred at 3.76 GHz are generated, with power of 3.2 GW, and efficiency of 34%. In the experiment, microwaves centered at 3.75 GHz are generated, with power of 2.5 GW, efficiency of 31%, repetition rate of 20 Hz and pulse duration above 110 ns. In the further experiment, a microwave with pulse duration above 200 ns is generated.

15:15 Mo-PM1-1-5
Mechanisms Of Submillimeter Wave Generation By Kiloampere REB In A Plasma Column With Strong Density Gradients
Andrey Arzhannikov; Vladimir Burmasov; Ivan Ivanov; Petr Kalinin; Sergey Kuznetsov; Maksim Makarov; Konstantin Mekler; Sergey Polosatkin; Andrey Rovenskikh; Denis Samtsov; Stanislav Sinitsky; Vasily Stepanov; Igor Timofeev
Budker Institute of nuclear physics SB RAS, Russian Federation

Project of powerful submillimeter wave generator based on intense interaction of a relativistic electron beam with a magnetized plasma is developed at BINP RAS in collaboration with NSU. In presented experiments, the beam with parameters 0.8 MeV/15 kA/6 ÃfÆ'Ã.½Ãfâ?sÃ,¼s is injected into a plasma column with the density ~ 1015 cm-3. Spectral composition of the emission from the plasma column is studied in the frequency band 0.1 -- 1 THz. In the analysis of the results of our studies we focus on the role of strong plasma density gradients in generation of sub-mm waves.

15:30 Mo-PM1-1-6
THz Cherenkov Oscillator With Surface-Radiating Modes
Eduard Khutoryan¹; Sergey Ponomarenko¹; Sergey Kishko¹; Yoshinori Tatematsu²; Seitaro Mitsudo²; Masahiko Tani²; Alexei Kuleshov^1
1O. Ya. Usikov Institute for Radiophysics and Electronics of NAS of Ukraine, Ukraine; ²Research Center for Development of Far-Infrared Region, Japan

In this paper, we present and discuss some operation modes arising in the oscillator with a sheet electron beam and a periodically modified grating. Special attention has been paid to the modes when surface plasmon polaritons are coupled to the radiating wave. The presented simulation results indicate high potential of the proposed oscillator for an efficient generation of THz radiation.

15:45 Mo-PM1-1-7
Simulation Of Secondary Electrons In A Megawatt-Class Gyrotron Collector With Voltage Depression And Magnetic Sweeping
Stephen Cauffman; Monica Blank; Philipp Borchard; Kevin Felch
CPI, United States

In megawatt-class gyrotrons, the residual energy of the electron beam must be dissipated in the collector without compromising the vacuum integrity of the device, necessitating the use of various methods for lowering the peak power density to acceptable levels. Secondary electron emission from the collector surface can redistribute the power deposition profile of the incident (primary) beam, which can either be beneficial or detrimental. Secondary electrons may also be re-accelerated toward the gyrotron body, and, if not magnetically reflected, may interfere with the operation of the interaction circuit. Here, simulations of a megawatt-class gyrotron collector, including the effects of voltage depression, magnetic sweeping, and secondary/reflected electrons, are presented, to assess the potential impact on gyrotron operation and longevity.

14:00-16:00 - Mo-PM1-2 - Solid State 2 - Petit Amphi

Chairperson: Christine Kadlec

14:00 Mo-PM1-2-1
Unveiling Temperature-Dependent Scattering Mechanisms In Semiconductor Nanowires Using Optical-Pump Terahertz-Probe Spectroscopy
Jessica Boland¹; Francesca Amaduzzi²; Sabrina Sterzl³; Heidi Potts²; Gözde Tütüncüoglu²; Laura Herz³; Anna Fontcuberta i Morral²; Michael Johnston^3
1University of Manchester, United Kingdom; ²École Polytechnique Fédérale de Lausanne, Switzerland; ³University of Oxford, United Kingdom

Optical-pump terahertz-probe (OPTP) spectroscopy is a powerful, non-contact tool for extracting the electrical conductivity within a material. In this work, we show how OPTP spectroscopy can be used to extract the temperature-dependent electron mobility and photoconductivity lifetime within semiconductor nanowires (NWs), in order to reveal the underlying scattering mechanisms governing carrier transport in these materials.

14:30 Mo-PM1-2-2
Time-Resolved THz Spectroscopy Of Metal-Halide Perovskite Single Crystals And Polycrystalline Thin Films
Chelsea Q. Xia¹; Qianqian Lin²; Jay B. Patel¹; Adam D. Wright¹; Timothy D. Crothers¹; Rebecca L. Milot³; Laura M. Herz¹; Michael B. Johnston^1
1University of Oxford, Clarendon Laboratory, United Kingdom; ²Wuhan University, School of Physics and Technology, Wuhan University, China; ³University of Warwick, Department of Physics, United Kingdom

In this study the photoconductivity and charge-carrier dynamics of the metal-halide perovskite MAPbI3 is investigated via optical-pump-THz-probe spectroscopy (OPTPS). We perform OPTPS on polycrystalline MAPbI3 thin films in both transmission and reflection modes, and demonstrate the consistency of extracted mobility and recombination parameters between the two geometries. Furthermore, we performed OPTP measurement on MAPbI3 single crystal in reflection and compare the mobility and charge recombination dynamics between the polycrystalline thin films and perovskite single crystals. Finally, the consequence of our results for future metal halide optoelectronic devices are discussed.

14:45 Mo-PM1-2-3
The Observation Of Spin Reorientation Phase Transition In Sm1-xErxFeO3
Yohei Koike; Kazumasa Hirota; Hongsong Qiu; Shodai Kimoto; Kosaku Kato; Masashi Yoshimura; Makoto Nakajima
Institute of Laser Engineering, Osaka University, Japan

Through the observation of magnetic resonance modes by terahertz time domain spectroscopy (THz-TDS) at the various temperature, we succeeded in observing spin reorientation phase transition (SRPT) which occurs at 310 K for Sm0.7Er0.3FeO3 single crystals. Furthermore, THz-pump and optical-Faraday-rotation measurement was introduced and the weak F-mode signals were successfully observed just below SRPT temperature.

15:00 Mo-PM1-2-4
Enhanced Generation Of THz Radiation In The Island Films Of Topological Insulators Bi2-xSbxTe3-ySey
Kirill Kuznetsov¹; Petr Kuznetsov²; Daniil Safronenkov¹; Alexey Temiryazev²; Galina Yakushcheva²; Galiya Kitaeva^1
1Lomonosov Moscow State University, Faculty of Physics, Russian Federation; ²Kotelnikov IRE RAS (Fryazino branch)

Using time-domain spectroscopy we studied the topological insulators, Bi2-xSbxTe3-ySey thin films of different thickness and chemical composition. The obtained temporal dependences of terahertz pulses show that generation of THz radiation is more effective in an island film with a total thickness of about tens of nanometers. For the first time an amplification of the THz radiation power by applying an external electric field to a topological insulator is demonstrated. This effect can be useful for fabricating photoconductive antennas based on topological insulators.

15:15 Mo-PM1-2-5
Analysis Of Glass Transition Temperatures In Indomethacin Polymer Mixtures
Adam Zaczek; Axel Zeitler
University of Cambridge, Department of Chemical Engineering and Biotechnology, United Kingdom

While drugs are typically created, stored, and administered in the more stable crystalline state, there is interest in industrial settings to stabilise amorphous pharmaceuticals to overcome bioavailability constraints. Terahertz time-domain spectroscopy (THz-TDS) can be used to determine how the glass transition temperatures directly relate to the stability of an amorphous sample. Indomethacin is an extensively studied anti-inflammatory, providing a benchmark sample for amorphous studies with terahertz spectroscopy. By mixing indomethacin with varying ratios of polymeric matrices, its amorphous stability can be increased, revealing trends in the THz-TDS results that directly relate to the potential energy surface of the system which provides insight into the interactions that occur within amorphous mixtures.

15:30 Mo-PM1-2-6
Coexistence Of Ferromagnetic And Superconducting Domains In Co-doped BaFe2As2 Superconductors Probed Using Infrared Faraday Measurements
Alok Mukherjee¹; Murat Arik¹; Jungryeol Seo¹; Hui Xing¹; Payam Taheri¹; Hao Zeng¹; Igor Mazin²; Hikaru Sato³; Hidenori Hiramatsu³; Hideo Hosono³; John Cerne^1
1University at Buffalo, Physics Dept., United States; ²Naval Research Laboratory, United States; ³Tokyo Institute of Technology, Japan

We explore the electronic and magnetic properties of superconducting iron pnictide films by probing their infrared Hall conductivity as a function of function of energy (0.1- 1.3 eV), temperature (10-300 K) and magnetic field (B = 0-7 T). We find hysteretic behavior in the complex infrared Faraday angle, θ_F, at low B over the entire temperature range. At higher B, θ_F is linear in B and we observe a peak in the high B-field slope near 50 K, which may be related to the superconducting Tc of the films.

15:45 Mo-PM1-2-7
THz Driven Dynamics In Mott Insulator GaTa4Se8
Elsa Abreu¹; Danylo Babich²; Etienne Janod²; Benoît Corraze²; Laurent Cario²; Steven Johnson^1
1ETH Zürich, Switzerland; ²Institut des Matériaux Jean Rouxel, Université de Nantes, France

GaTa4Se8 is a Mott insulator known to exhibit an electric Mott transition, characterized by a drop in electrical resistivity, when an electric field larger than 1 -- 10 kV/cm is applied for a few tens of microseconds using electrodes deposited on the sample. Here, we show that a resistivity drop can be induced in this material within less than a picosecond. These dynamics occur after excitation by a high field THz pump pulse and persist for a few picoseconds, well beyond the duration of the pump pulse.

14:00-16:00 - Mo-PM1-3 - Ultrafast - Room 269

Chairperson: Juliette Mangeney

14:00 Mo-PM1-3-1

Terahertz Pulse Trapping Beyond The Delay-Bandwidth Limit
Nima Chamanara¹; Lauren Gingras¹; Aidan W. Schiff-Kearn¹; Jean-Michel Ménard²; David G. Cooke^1
1McGill University, Canada; ²University of Ottawa, Canada

We demonstrate the trapping of a broadband THz pulse in a cavity with dynamic walls created faster than the cavity transit time. The trapping bandwidth and dwell time within the cavity, formed by patterned fs photoexcitation of reflective metallic regions within a silicon filled parallel plate waveguide, is shown to violate the delay-bandwidth limit of a passive resonator.

14:30 Mo-PM1-3-2
Ultrafast Metallization In NbO2 Studied By Pump-probe THz Spectroscopy
Rakesh Rana; J. Michael Klopf; Jörg Grenzer; Harald Schneider; Manfred Helm; Alexej Pashkin
Helmholtz-Zentrum Dresden-Rossendorf, Germany

Niobium dioxide (NbO2) is an isovalent counterpart of VO2 with a considerably higher transition temperature (TC = 1080 K). We have performed time-resolved optical pump -- THz probe measurements on a NbO2 epitaxial thin film at room temperature. Notably, the pump energy required for the switching into a metastable metallic state is smaller than the energy necessary for heating NbO2 up to Tc providing strong evidence for the non-thermal character of the photoinduced insulator-to-metal transition.

14:45 Mo-PM1-3-3
Ultrafast Dynamics Of Hydroxyl Radical Observed By Its FID Radiation In Magnetic Field
Vitaly Kubarev¹; Evgeniy Chesnokov²; Lev Krasnoperov³; Pavel Koshlyakov^2
1Budker Institute of Nuclear Physics, Russian Federation; ²Institute of Chemical Kinetics and Combustion, Russian Federation; ³New-Jersey Institute of Technology, United States

Ultrafast dynamics of OH radical was investigated by its Free Induction Decay (FID) signal. In our experiments doublet rotational line of the radical was excited by pulse of free-electron laser. Effect of a magnetic field on polarization of the FID was studied by numerical simulation. Experimental investigations of the magnetic field effect is in progress now.

15:00 Mo-PM1-3-4
Terahertz Spectroscopy To Unveil Intraband Scattering In Photoexcited Graphene
Srabani Kar¹; Stephanie Adeyemo¹; Ajay Sood²; Hannah Joyce^1
1University of Cambridge, United Kingdom; ²Indian Institute of Science, Department of Physics, India

Intraband scattering dynamics of optically excited graphene has been explored by using time resolved terahertz spectroscopy. The results for different forms of graphene in terms of layers, Fermi energy position, hydrogen functionalization have been discussed and explained by using Boltzmann transport theory. It is shown how the short-range and Coulomb scattering play important roles in determining photoinduced terahertz conductivity. Photoexcited bilayer graphene showed transition from negative to positive photo-induced terahertz conductivity in the spectral range 0.5-2.5 THz. It is revealed that short-range scattering plays the most significant role to determine the ultrafast photocondcutivity of graphene at terahertz range. However, at low doping state, Coulomb scattering contribute significantly to the imaginary part of conductivity.

15:15 Mo-PM1-3-5
Nonlinearity Of Ultrafast Anomalous Hall Currents In GaAs
Christoph Dresler; Mark Bieler
PTB-The National Metrology Institute of Germany, Germany

PTB-The National Metrology Institute of Germany, PTB-The National Metrology Institute of Germany, Bundesallee 100, Germany
We induce ultrafast anomalous Hall currents in GaAs by optical femtosecond excitation at various temperatures and magnetic fields. The currents' dynamics is studied by detecting the simultaneously emitted THz radiation. A linear behavior is obtained at room temperature and low magnetic fields. However, at higher magnetic fields and, in particular, at low temperatures, we enter a highly nonlinear regime, in which the current dynamics drastically varies. Most likely, this variation results from different microscopic mechanisms which compete against each other

15:30 Mo-PM1-3-6
THz Response Of Metallic Structures To Femtosecond Laser Pulses
Ivan Oladyshkin; Daniil Fadeev; Vyacheslav Mironov
Institute of Applied Physics of the Russian Academy of Sciences, Russian Federation

The talk is devoted to the nonlinear effects in metallic structures (like gratings and nanoparticle arrays) irradiated by intense femtosecond laser pulses. Possible mechanisms of delayed THz response and specific non-quadratic nonlinear regimes of conversion are analyzed. In contrast to previous models, only low-frequency currents inside the metal are considered without involving electron emission and acceleration. Special attention is paid to the role of plasmonic resonances at optical frequency in the enhancement of low-frequency nonlinear response.

15:45 Mo-PM1-3-7
Surface THz Emission From Germanium
Ignas Nevinskas; Ričardas Norkus; Arūnas Krotkus

Center for Physical Sciences and Technology, Lithuania

Terahertz emission from germanium after femtosecond laser pulse excitation is a result of the photo-Dember effect and the built-in surface electric field. The indirect band gap semiconductor is investigated with various excitation wavelengths and different dopant types to differentiate these mechanisms. THz pulse emission is observed even at exciting quanta energies lower than the direct band gap. The azimuthal angle dependences suggest a 3rd order optical nonlinearity.

14:00-16:00 - Mo-PM1-4 - 2D Materials 1 - Room 162

Chairperson: Berardi Sensale Rodriguez

14:00 Mo-PM1-4-1

THz Excited State Level Spacing In Encapsulated Graphene Quantum Dots
Elisa Riccardi; Sylvain Massabeau; Federico Valmorra; Michael Rosticher; Jerome Tignon; Takis Kontos; Sebastien Balibar; Sukhdeep Dhillon; Robson Ferreira; Juliette Mangeney
Laboratoire de Physique de l'Ecole Normale Superieure, France

We report a high-quality encapsulated graphene quantum dot that exhibits stable Coulomb diamonds and excited states with a spacing of 0.5 THz. The quantum dot is connected to a bow tie antenna for measurements under THz illumination. The experimental set-up includes a dilution cryostat operating at temperature T<200mK with optical access at THz frequencies.

14:30 Mo-PM1-4-2
PT-Symmetric Terahertz Photoconductivity In Hg1-xCdxTe
Dmitry Khokhlov¹; Akeksei Kazakov¹; Alexandra Galeeva¹; Aleksei Artamkin¹; Ludmila Ryabova¹; Sergey Dvoretsky²; Nikolay Mikhailov²; Mikhail Bannikov³; Sergey Danilov⁴; Sergey Ganichev^4
1M.V. Lomonosov Moscow State University, Russian Federation; ²A.V. Rzhanov Institute of Semiconductor Physics of SB RAS, Russian Federation; ³P.N. Lebedev Physical Institute of RAS, Russian Federation; ⁴University of Regensburg, Germany

We show that the terahertz photoconductivity in Hg1-xCdxTe-based films with the inverted band structure corresponding to the topological phase is asymmetric in magnetic field which may be considered as T-symmetry breaking. Beside that, the photoconductivity is asymmetric for two mirror-symmetric pairs of potential probes which may be treated as P-symmetry breaking. At the same time, the photoconductivity remains intact upon simultaneous swapping of both magnetic field and potential probe couple revealing thus the PT-symmetry.

14:45 Mo-PM1-4-3
Conductivity Measurement Of Graphene On Thin Polymeric Film By Broadband Air-plasma THz Spectroscopy
Binbin Zhou; Qian Shen; Patrick Whelan; Lujun Hong; Peter Jepsen
DTU Fotonik, Technical University of Denmark, Denmark

The sheet conductivity of graphene on thin polymer film can be accurately measured by air-plasma based ultra-broadband terahertz time-domain spectroscopy (THz-TDS). The transmitted THz echo signals are well separated in time due to the short THz pulse duration, and oscillation-free frequency dependent conductivity curves can be obtained.

15:00 Mo-PM1-4-4
Unveiling The Plasma Wave In The Channel Of Graphene Field-effect Transistor
Amin Soltani¹; Frederik Kuschewski²; Marlene Bonmann³; Andrey Generalov⁴; Andrei Vorobiev³; Florain Ludwig¹; Matthias M. Wiecha¹; Dovilė Čibiraitė¹; Frederik Walla¹; Susanne C. Kehr²; Lucas M. Eng²; Jan Stake³; Hartmut G. Roskos^1
1Goethe University Frankfurt, Germany; ²University of Technology, Dresden, Germany; ³Chalmers University of Technology, Sweden; ⁴Aalto University, Finland

Coupling an electromagnetic wave at GHz to THz frequencies into the channel of a graphene field-effect transistor (GFET) provokes collective charge carrier oscillations of the two-dimensional electron gas (2DEG) known as plasma waves. Here, we report the very first experimental and direct mapping of the electric field distribution in a gated GFET at nanometer length scales using scattering-type scanning near-field microscopy (s-SNOM) at 2 THz. Based on the experimental results we deduce the plasma wave velocity for different gate bias voltages, which is in good agreement with the theoretical prediction.

15:15 Mo-PM1-4-5
Excitation And Amplification Of The Unidirectionally Propagating Terahertz Plasmon In A Periodical Graphene Structure
Denis Fateev; Ilya Moiseenko; Konstantin Mashinsky; Viacheslav Popov
Kotelnikov Institute of Radio Engineerin and Electronics, Russian Academy of Science, Russian Federation

The amplification of the unidirectionally propagating plasmon modes excited by the incident terahertz wave in a periodical structure with an active graphene is studied theoretically. The amplification of propagating plasmon modes is due to radiative recombination in inverted graphene.

15:30 Mo-PM1-4-6
Experimental Investigation Of Graphene Layers As 2D Nanoelectrode For Continuous Wave Terahertz Generation
Alaa Jumaah; Shihab Al-Daffaie; Oktay Yilmazoglu; Franko Küppers; Thomas Kusserow
Technische Universität Darmstadt, Germany

The 2D photomixer investigation showed enhanced photocurrent for high THz output power. The number of graphene layers' effect directly the electrical and optical properties of the device. Higher transparency of a thinner graphene increased the illuminated effective area to increase the number of the generated carries. However, a thicker graphene is required to carry high current density and enhance the photomixer performance.

15:45 Mo-PM1-4-7
Modulation Behaviors, Conductivities, And Carrier Dynamics Of Single And Multilayer Graphenes
Emine Kaya¹; Nurbek Kakenov²; Coskun Kocabas²; Hakan Altan²; Okan Esenturk^2
1Middle East Technical Univeristy, Turkey; ²Bilkent University, Turkey

Time domain and time resolved terahertz studies of single- and multi-layer graphene (SLG and MLG) samples and modulator devices will be presented. A high performance up to 100% of modulators were observed with the devices even at very low voltages. High modulation depth over such a broad spectrum and simple device structure brings significant importance toward application of this type of device in THz and related technologies. In addition, conductivities of SLG and MLG devices were also investigated and a change in behavior was observed as the layer thickness increased. The charge carriers dynamics of the samples with pulp fluence and color was also highly interesting.

14:00-16:00 - Mo-PM1-5 - THz TDS 2 - Room 151

Chairperson: Mona Jarrahi

14:00 Mo-PM1-5-1

THz TDS System With 105 DB Dynamic Range Based On Transition Metal Doped InGaAs
Robert Kohlhaas¹; Steffen Breuer¹; Simon Nellen¹; Lars Liebermeister¹; Martin Schell¹; Mykhaylo Semtsiv²; William Masselink²; Björn Globisch^1
1Fraunhofer HHI, Germany; ²Humboldt University Berlin, Germany

A THz time-domain spectroscopy (TDS) system is presented, which uses photoconductive antennas made of iron and rhodium doped InGaAs. Due to the unique combination of ultrashort lifetime and high mobility as well as high resistivity, the transition metal doped InGaAs surpasses the performance of state-of-the-art photoconductors when applied as THz antennas: The presented THz TDS system features a spectral bandwidth of 6.5 THz and a dynamic range of up to 105 dB.

14:30 Mo-PM1-5-2
Comb-locked Frequency-domain Terahertz Spectrometer
Thomas Puppe; Yuriy Mayzlin; Julian Robinson-Tait; Rafal Wilk
TOPTICA Photonics AG, Germany

We introduce a frequency-domain spectrometers (FDS) based on a comb locked optical frequency synthesizer which combines scanning ranges of more than 3 THz at scan rates >300 GHz/s with frequency resolution in the order of 10 kHz. The comb provides a narrow linewidth spectrum which is absolutely referenced to a frequency standard (e.g. GPS). The inherent stability allows for favorable signal-to-noise scaling with measurement time.

14:45 Mo-PM1-5-3
Rapid Thickness Measurement With A SLAPCOPS-based Terahertz TDS System
Michael Kolano; Oliver Boidol; Daniel Molter; Georg von Freymann
Fraunhofer ITWM, Germany

Terahertz time-domain spectroscopy traditionally requires either one mode-locked laser and an external delay line or two mode-locked lasers with a controllable repetition rate difference. Here we demonstrate a polarization-multiplexed single-laser system, which combines the benefits of both approaches without any external delay line. The fiber laser emits two pulse trains with independently adjustable repetition rates, utilizing only one laser-active section and one pump diode. With a standard fiber-coupled terahertz setup, we are able to measure transients with a spectral bandwidth of 2.5 THz and a dynamic range of 50 dB in a measurement time of 1 s. An additional benefit of the underlying concept is the possibility for the rapid measurement of very thick samples usually not possible with traditional single-laser systems.

15:00 Mo-PM1-5-4
Deep Learning Approach For Removal Of Water Vapor Effects From THz-TDS Signals
Mikhail Mikerov; Jan Ornik; Martin Koch
Philipps-University Marburg, Germany

We propose a new very fast technique for the post-measurement removal of the water vapor effect on THz-TDS signals. Due to its very fast execution time and good generalization ability this technique has the potential to become an alternative to performing the measurements under dry atmosphere.

15:15 Mo-PM1-5-5
Terahertz Time-Domain Spectroscopy Up To 20 THz Based On Organic Electro-Optic Crystals
Mojca Jazbinsek¹; Tobias Bach²; Uros Puc¹; Vincent Michel¹; Carolina Medrano²; Peter Gunter^2
1Zurich University of Applied Sciences (ZHAW), Switzerland; ²Rainbow Photonics AG, Switzerland

We demonstrate ultrabroadband THz-wave generation and detection in a compact system based on a femtosecond fiber laser at 1560 nm and optical rectification in organic electro-optic crystals DSTMS. Terahertz time-domain spectroscopy with a spectrum extending up to 20 THz with a maximum bandwidth exceeding 70 dB is possible with this system.

15:30 Mo-PM1-5-6
Terahertz Time-domain Magneto-optic Spectroscopy Without The Polarization-resolution Technique
Masaya Nagai; Atsushi Nakane; Hiroyasu Suzukawa; Tomohide Morimoto; Masaaki Ashida
Osaka University, Japan

We propose a simple method for magneto-optic spectroscopy in the terahertz frequency regime without the conventional polarization-resolution technique. It is based on the time-domain reflection spectroscopy and employs circularly polarized terahertz light with magnetic field modulation. We experimentally demonstrate it for an InAs substrate. Our demonstration will help to advance multi-purpose characterization techniques for various semiconductors.

15:45 Mo-PM1-5-7
Characterization Of Thin Film Liquids By Multilayer Structure In THz Time Domain Reflection Spectroscopy
Qiushuo Sun¹; Xuequan Chen¹; Kai Liu¹; Xudong Liu²; Arturo Hernandez-Serrano³; Emma Pickwell-MacPherson^3
1the Chinese University of Hong Kong, Hong Kong; ²Shenzhen University, China; ³University of Warwick, United Kingdom

The characterization of thin film liquids is not as straightforward as bulk materials, as it requires accurate control of the thin film thickness and precise measurements of the amplitude and phase of the signals. We propose a multilayer structure for terahertz (THz) time domain reflection spectroscopy (TDRS) characterization of thin film liquids, the equations for this geometry are derived and the water-ethanol mixtures with various concentrations are measured, the refractive indices and absorption coefficients extracted from the proposed geometry and ordinary bulk reflection geometry match well. This work demonstrates that the proposed multilayer structure can be used to extract the optical properties of liquids by using a tiny amount of the sample, it can be potentially applied to characterize valuable biological aqueous solutions in the future.

14:00-16:00 - Mo-PM1-6 - QCL 2 - Room 101

Chairperson: Martin Wienold

14:00 Mo-PM1-6-1

Frequency Noise And Phase-locking Of A Quantum Cascade Laser-pumped, 1.073THz Molecular Laser Using A 1560nm Frequency Comb
Stefano Barbieri¹; Jean-Francois Lampin¹; Antoine Pagies¹; Giorgio Santarelli²; Hesler Jeffrey³; Wolfgang Hansel⁴; Ronald Holzwarth^4
1IEMN - CNRS Laboratory, France; ²Laboratoire LP2N - CNRS, France; ³Virginia Diodes Inc., United States; ⁴Menlo Systems GmbH, Germany

We report the measurement of the frequency noise power spectral density (PSD) of a THz molecular laser (ML) pumped by a mid-infrared (MIR) quantum cascade laser (QCL). This is obtained by beating the ML frequency with the harmonic of the repetition rate of a 1560nm frequency comb (FC). We find a frequency noise PSD < 10Hz2/Hz (-95dBc/Hz) at 100kHz from the carrier, limited by the noise of the QCL current driver. We also show that it is possible to actively phase-lock the QCL-pumped ML to the FC repetition rate harmonic by controlling the QCL drive current.

14:30 Mo-PM1-6-2
High-resolution Frequency And Phase Control Of A Terahertz Laser
Reshma A Mohandas¹; Alwyn Seeds²; Edmund Linfield¹; Giles Davies¹; Paul Dean¹; Lalitha Ponnampalam²; Joshua Freeman^1
1University of Leeds, School of Electronic and Electrical Engineering, United Kingdom; ²University College London, School of Electronic and Electrical Engineering, United Kingdom

We report on the high-resolution frequency and phase control of a terahertz (THz) quantum cascade laser (QCL). The 2.0 THz QCL is locked to a stable microwave reference frequency via an all-fibre infrared frequency comb. The frequency of the QCL is controlled by optical injection and the phase is independently controlled by introducing a phase-lock loop that provides electronic feedback to the QCL, forming an optical injection phase locked loop (OIPLL). By implementing this, for a fixed frequency, (1) the phase of the THz QCL relative to the microwave reference frequency can be controlled within a range 0.3Ãfââ?s¬, (2) the linewidth of the locked QCL was <1Hz (instrument limited) (3) the frequency and phase was stabilised for longer timescales.

14:45 Mo-PM1-6-3
Dispersion Measurements Of Terahertz Quantum Cascade Fabry-Perot Cavities And VECSELs
Tudor Olariu; Mattias Beck; Jerome Faist; Giacomo Scalari
ETH Zurich, Switzerland

A method for obtaining the dispersion of terahertz (THz) quantum cascade lasers (QCL) is presented. By measuring the relative phase of the center burst and first satellite peak within the interferogram of a sub-threshold THz QCL emitting cavity inside a Fourier Transform Infrared Spectrometer (FTIR), the electroluminescence spectrum is determined by Fourier Transform and the group velocity dispersion can be calculated. This method is applicable to any QCL -- here shown for Fabry-Perot (FP) ridge laser as well as VECSEL.

15:00 Mo-PM1-6-4
THz Quantum Cascade Lasers Operating Up To 210 K
Martin Franckie¹; Lorenzo Bosco¹; Mattias Beck¹; Elena Mavrona¹; Andreas Wacker²; Jerome Faist^1
1ETH Zürich, Switzerland; ²Lund Univsersity, Sweden

We present THz QCLs based on two quantum wells per period, designed and optimized with a nonequilibrium Green's function model, which lase up to 210 K cryostat temperature using a dry etched Cu-Cu double-metal waveguide

15:15 Mo-PM1-6-5
THz Quantum Cascade Laser Frequency Combs
Francesco Mezzapesa¹; Katia Garrasi¹; Valentino Pistore²; Lianhe Li³; A. Giles Davies³; Edmund Linfield³; Sukhdeep Dhillon²; Miriam Vitiello^1
1NEST, CNR - Istituto Nanoscienze and Scuola Normale Superiore, Italy; ²Laboratoire Pierre Aigrain, Departement de physique de l'ENS, France; ³School of Electronic and Electrical Engineering, University of Leeds, United Kingdom

We demonstrate THz optical frequency comb (FC) operation based on ultra-broadband, record dynamic range Quantum Cascade Lasers (QCLs) which exploit a heterogeneous active region design to achieve low and flat chromatic dispersion at the center of the gain curve. By implementing a Gires-Tournois Interferometer (GTI), as tightly coupled at one end of the QCL cavity, we provide lithographically-independent control of the free-running coherence properties of such THz-QCL FC and attain wide dispersion compensation regions, where stable and narrow (~3 kHz linewidth) single beatnotes extend over an operation range that is significantly larger than that of dispersion-dominated bare laser cavity counterparts.

15:30 Mo-PM1-6-6
Gain Dynamics In THz QCLs And Its Implication For THz Comb Sources
Christian Georg Derntl¹; Dominik Theiner¹; Giacomo Scalari²; Mattias Beck²; Jérôme Faist²; Karl Unterrainer¹; Juraj Darmo^1
1TU Wien, Photonics Institute, Austria; ²ETH Zürich, Institute of Quantum Electronics, ETH Zürich, Switzerland

In this contribution we present investigation of the interactions between the individual quantum cascade sections of a heterogeneous terahertz quantum cascade laser and their role in the stable operation of a broadband gain material. We employed THz-pump/THz-probe time domain spectroscopy (TDS) and reveal the spectrally resolved gain recovery time for each quantum cascade section that has multi-exponential decay character. Obtained results are discussed with respect to a frequency comb formation.

15:45 Mo-PM1-6-7
Self-Mixing Interferometry In Continuous-Wave High Power 1D And 2D QCL Random Lasers Operating At Terahertz Frequencies
Kimberly Reichel¹; Simone Biasco²; Teresa Crisci¹; Katia Garrasi¹; Francesco Mezzapesa¹; Miriam Vitiello^1
1NEST, CNR-Nano, Italy; ²NEST, Scuola Normale Superiore, Italy

We observe the first evidence of self-mixing in THz frequency quantum cascade random lasers fabricated in both wire and irregularly squared resonator architectures with surface photonic patterns. By reflecting the emitted light back into the laser cavity and changing the external cavity length, we observe the interference fringes within the laser cavity, thereby proving evidence of self-mixing. This paves the way to detectorless speckle-free imaging applications in the far-infrared.

15:45-16:15 - Coffee Break

16:30-18:15 Parallel sessions Mo-PM2

16:30-18:15 - Mo-PM2-1 - Gyrotron 3 - Amphi Lavoisier

Chairperson: Mikhail Glyavin

16:30 Mo-PM2-1-1
Development Of A Second Harmonic Multi-Frequency Gaussian Beam Output Gyrotron FU CW GVII
Yoshinori Tatematsu¹; Kyoya Takayama²; Yuto Maeda²; Tatsuya Ueyama²; Taisei Ogura²; Kazuki Nakagawa²; Ryota Kamiya²; Masafumi Fukunari²; Yuusuke Yamaguchi²; Teruo Saito^2
1FIR center, University of Fukui, Japan; ²University of Fukui, Japan

A sub-THz second harmonic multi-frequency gyrotron with Gaussian beam output, Gyrotron FU CW GVII, has been developed. This gyrotron was designed to change the frequency stepwise in the range from 270 to 420 GHz. Oscillations of seven second-harmonic modes were successfully observed and Gaussian beam radiations converted from six oscillation modes were observed. Two second harmonic modes; TE65 and TE85; oscillated in a single mode. Even in case of simultaneous oscillation of fundamental modes, radiation beams converted from second harmonic modes can be separated from the fundamental mode beams by making use of the different radiation directions emitted from the gyrotron window.

17:00 Mo-PM2-1-2
ECRH With 10 Gyrotrons At W7-X -- Achievements And Enhancements
Harald Braune; H.P. Laqua; K.J. Brunner; S. Marsen; D. Moseev; F. Noke; F. Purps; N. Schneider; T. Schulz; T. Stange; P. Uhren; F. Wilde; M. Zanini
Max-Planck-Institut für Plasmaphysik, Germany

Electron Cyclotron Resonance Heating (ECRH) was the main heating system during the operation campaign OP1.2b in 2018 of the W7-X stellarator [1]. The steady state capable ECRH system was used for plasma start-up, X-mode and O-mode heating as well as current drive (ECCD). The ECRH plant is equipped with 10 operational 140 GHz gyrotrons and a quasi-optical transmission line, which is operated under standard atmosphere conditions. The achieved plasma parameters with respect to the performance of the ECRH plant and prospective enhancements will be discussed

17:15 Mo-PM2-1-3
A 35GHz 100kW Klystron Amplifier Design
Fang Zhu
Institute of Electronics, Chinese academy of sciences, China

We present the design and modelling of a five-cavity, high-power klystron operating in Ka-band and paced with permanent magnet focusing system. The amplifier is powered by an electron gun operating at a voltage of 40 kV and a total current of 6 A. The circuit is comprised of four single-gap cavities and a three-gap extended interaction output cavity operating in the ?-mode. The main predicted characteristics of the klystron includes a 100 kW peak power at 35GHz, an efficiency of 40% and 42 dB gain.

17:30 Mo-PM2-1-4
Microwave-Band Chirped Pulse Amplification Technique Based On A System Of Helically Corrugated Waveguides
Irina Zotova; Naum Ginzburg; Lev Yurovskiy; Michael Vilkov; Alexander Sergeev; Sergey Samsonov; Alexander Bogdashov
Institute of Applied Physics RAS, Russian Federation

We consider the possible implementation of the Chirped Pulse Amplification (CPA) technique, widely used in optics, for the microwave frequency band. We propose using helically-corrugated waveguides for pulse stretching and compressing as their dispersion properties strongly depend on geometrical parameters. For stretched pulse amplification, a helical-waveguide gyro-TWT can be used as a broadband amplifier. Simulations with parameters of the experimentally realized 30 GHz gyro-TWT show that for a 300 W, 200 ps incident pulse, amplification up to 4 MW (40 dB) can be achieved in this system, while in the linear regime of the same gyro-TWT the output power is only about 250 kW.

17:45 Mo-PM2-1-5

Completion Of The 8 MW Multi-Frequency ECRH System at ASDEX Upgrade
Dietmar Wagner¹; Jörg Stober¹; Michael Kircher¹; Fritz Leuterer¹; Francesco Monaco¹; Max Münich¹; Martin Schubert¹; Hartmut Zohm¹¹; Gerd Gantenbein²; John Jelonnek²; Manfred Thumm²; Andreas Meier²; Theo Scherer²; Dirk Strauss²; Walter Kasparek³; Carsten Lechte³; Burkhard Plaum³; Alexander Zach³; Alexander Litvak⁴; Gregory Denisov⁴; Alexey Chirkov⁴; Vladimir Malygin⁴; Leonid Popov⁵; Vadim Nichiporenko⁵; Vadim Myasnikov⁵; Evgeny Tai⁵; Elena Solyanova^5
1Max-Planck-Institut für Plasmaphysik, Germany; ²Karlsruhe Institute of Technology, Germany; ³Universität Stuttgart, Germany; ⁴Insitute of Applied Physics, Russian Federation; ⁵Gycom Ltd, Russian Federation

Over the last 15 years, the Electron Cyclotron Resonance Heating (ECRH) system at the ASDEX Upgrade tokamak has been upgraded from a 2 MW, 2 s, 140 GHz system to an 8 MW, 10 s, dual frequency system (105/140 GHz). Eight gyrotrons were in routine operation during the current experimental campaign. All gyrotrons are step-tunable operating at 105 and 140 GHz with a maximum output power of about 1 MW and 10 s pulse length. The system includes 8 transmission lines, mainly consisting of oversized corrugated waveguides (I.D. = 87 mm) with overall lengths between 50 and 70 meters including quasi-optical sections at both ends. Further improvements of the transmission lines with respect to power handling and reliability are underway.

18:00 Mo-PM2-1-6
High-Gradient Test Results Of W-Band Accelerator Structures
Mohamed Othman¹; Julian Picard²; Samuel Schaub²; Valery Dolgashev¹; Sudheer Jawla²; Emma Snively¹; Bruno Spataro³; Richard Temkin²; Sami Tantawi¹; Emilio Nanni^1
1SLAC National Accelerator Laboratory, United States; ²Massachusetts Institute of Technology, United States; ³INFN-LNF, Italy

We report high-gradient test results for a 110 GHz single-cell standing wave accelerating cavity powered by a 1 MW gyrotron. The cavity is fed with 10 ns, 100s of kilowatt pulses, and achieved a field gradient up to 225 MV/m.

16:30-18:30 - Mo-PM2-2 - Solid State 3 - Petit Amphi

Chairperson: Manfred Helm

16:30 Mo-PM2-2-1
Terahertz Anomalous Hall Effect In Mn2-xPtSn
Di Liu¹; Artem Pronin¹; Anastasios Markou²; Claudia Felser²; Martin Dressel^1
1Universität Stuttgart, Germany; ²Max-Planck-Institute for Chemical Physics of Solids, Germany

Coherent-source THz spectroscopy was employed for measuring the Faraday rotation angle of Mn2-xPtSn films (x = 0; 0.2). In the THz experiments, we observe clear signatures of an anomalous Hall state, while any indications of the so-called topological Hall effect -- recently observed in these magnetically disordered systems in dc measurements - are absent. This demonstrates that the charge scattering mechanisms, responsible for the two phenomena, possess very different time scales: the anomalous Hall state is governed by the scattering process with the rates above THz frequencies, while the electron interaction, providing the topological Hall, possesses very low characteristic time scales.

17:00 Mo-PM2-2-2
Nonlinear Modulation Of Optical Absorption In Orthoferrites Due To Spin Precession Induced By Intense Terahertz Magnetic Field
Takayuki Kurihara¹; Motoaki Bamba²; Tohru Suemoto^3
1University of Konstanz, Germany; ²PRESTO, Japan Science and Technology Agency, Japan; ³Toyota Physical and Chemical Research Institute, Japan

We probe the transient change of near-infrared optical absorption in orthoferrites induced by coherent spin precession motion due to intense terahertz (THz) excitation. It has been found that under strong incident THz magnetic field strengths, the time profile of absorption exhibits periodic oscillation that is double the frequency of impulsively excited spin precession. The observed phenomena can be described by dielectric function which involves spin-spin exchange interaction. Our result demonstrates the potential of intense THz magnetic field in observing and controlling the fundamental interactions in magnetically ordered materials.

17:15 Mo-PM2-2-3
Ultrafast Terahertz Magnetometry
Wentao Zhang¹; Pablo Maldonado²; Zuanming Jin³; Keno Krewer¹; Jacek Arabski⁴; Guy Schmerber⁴; Eric Beaurepaire⁴; Tobias Kampfrath⁵; Mischa Bonn¹; Peter Oppeneer²; Dmitry Turchinovich^6
1Max Planck Institute for Polymer Research, Germany; ²Uppsala University, Sweden; ³Shanghai University, China; ⁴Institut de Physique et Chimie des Matériaux de Strasbourg, France; ⁵Freie Universität Berlin, Germany; ⁶Universität Bielefeld, Germany

THz emission spectroscopy is a powerful tool to access ultrafast magnetization dynamics in laser-excited magnetic systems. Here, we demonstrate femtosecond terahertz magnetometry, a method that can be used to rigorously reconstruct the (sub)picosecond-timescale magnetization dynamics in photoexcited ferromagnetic nanofilms from the magnetically-driven THz emission. Considering the propagation of the THz field from the surface of the film to the THz electro-optic sampling unit, we establish the transfer function, which allows us to obtain the ultrafast magnetization dynamics in the laser-excited sample in a calibrated manner.

17:30 Mo-PM2-2-4
Terahertz Pulsed-field Magneto-spectrometer At Room-temperature
Jean-Francois Lampin¹; Antoine Pagies¹; Stefano Barbieri¹; Ludovic Desplanque¹; Xavier Wallart¹; Jeffrey Hesler²; Oleksiy Drachenko³; Jean Leotin^3
1IEMN-CNRS, France; ²Virginia Diodes, United States; ³LNCMI, France

We have developed a compact pulsed-field THz magneto-spectrometer based on a THz molecular laser and heterodyne detection both at room-temperature. The recently developed continuous-wave THz laser uses mid-IR-pumped ammonia as active medium. The receiver is based on a subharmonic mixer pumped by a multiplication chain. A pulsed magnetic field up to 9 T is supplied by discharging a capacitor in a small coil at room-temperature. We demonstrate here the use of this spectrometer by measuring the effective mass of electrons in an InAs/AlGaSb heterostructure at room-temperature.

17:45 Mo-PM2-2-5
Magnon-polaritons In Dysprosium Ferrite
Marcin Bialek; Arnaud Magrez; Jean-Philippe Ansermet
Institute of Physics, Ecole Polytechnique Fédérale de Lausanne (EPFL), Switzerland

We report on an experimental observation of a coupling of magnons with cavity photons at THz frequencies in an antiferromagnet dysprosium ferrite (DyFeO3). We show that magnon-polaritons can be observed and controlled in antiferromagnets. This brings the existing research on magnon-photon coupling to THz frequencies, because antiferromagnets have their magnetic resonances in this range even without external magnetic fields.

18:00 Mo-PM2-2-6
Magnetoelectric Excitations In Polar Antiferromagnetic Nickel Tellurates Substituted By Mn And Co
Christelle Kadlec¹; Stella Skiadopoulou¹; Maria Retuerto²; Filip Kadlec¹; Fedir Borodavka¹; Martin Misek¹; Martha Greenblatt²; Stanislav Kamba^1
1Institute of Physics CAS, Czech Republic; ²Department of Chemistry and Chemical Biology, Rutgers, The State University of New Jersey, United States

By a combination of infrared, Raman and time-domain THz spectroscopies, we studied spin and lattice excitations in Ni3TeO6 and its isostructural compounds obtained by substitution of Ni with Mn or Co. Low-temperature THz spectra revealed THz-range excitations sensitive to magnetic field; some of them can be assigned to electromagnons.

18:15 Mo-PM2-2-7
Ultrafast Magnetic Response In ε-Fe2O3 Nano Magnet Measured By Terahertz-pump Optical-Faraday-probe Measurement
MAKOTO NAKAJIMA¹; Hongsong Qiu¹; Shodai Kimoto¹; Kosaku Kato¹; Yohei Koike¹; Masashi Yoshimura¹; Kenta Imoto²; Marie Yoshikiyo²; Asuka Namai²; Seiji Miyashita²; Shin-ichi Ohkoshi^2
1Osaka University, Japan; ²the university of Tokyo, Japan

Ultrafast magnetic response in epsilon-iron oxide (ε-Fe2O3) nano magnet was measured by terahertz-pump optical Faraday probe measurement. Terahertz excitations induce the extremely fast response of the magnetization. The response time is within 400 fs which corresponds to the time duration of the terahertz pulses.

16:30-18:15 - Mo-PM2-3 - High Fields 1 - Room 269

Chairperson: Jozsef Fulop

16:30 Mo-PM2-3-1

Strong-field THz Nonlinearity On Gold Nanofilms

Tianshu Hong¹; Bing Song¹; Chen Ouyang³; Baolong Zhang³; Jungang Miao¹; Yutong Li²; Xiaojun Wu^{1 1}School of Electronic and Information Engineering, Beihang University, China; ²School of Physical Sciences, University of Chinese Academy of Sciences, China; ³School of Physical Sciences, University of Chinese Academy of Sciences, China

In summary, we show the nonlinearity of strong-field terahertz radiation on gold nanofilms, and propose that this phenomenon can be explained by the terahertz-induced electron delocalization in the gold nanostructures.

17:00 Mo-PM2-3-2
Terahertz-driven Acceleration Of A Relativistic 35 MeV Electron Beam
Morgan Hibberd¹; Alisa Healy²; Daniel Lake³; Vasileios Georgiadis¹; Elliott Smith⁴; Oliver Finlay³; Thomas Pacey⁵; James Jones⁵; Yuri Saveliev⁵; David Walsh⁵; Edward Snedden⁵; Robert Appleby⁴; Graeme Burt²; Darren Graham¹; Steven Jamison^3
1School of Physics and Astronomy & Photon Science Institute, The University of Manchester, United Kingdom; ²Department of Engineering, Lancaster University,United Kingdom; ³Department of Physics, Lancaster University, United Kingdom; ⁴School of Physics and Astronomy, The University of Manchester, United Kingdom; ⁵Accelerator Science and Technology Centre, Science and Technology Facilities Council, United Kingdom

We will present the first results from the CLARA research facility at Daresbury Laboratory demonstrating terahertz-driven acceleration of a relativistic 35 MeV electron beam. A polarization-tailored, frequency-tunable, narrowband terahertz source was used to directly excite the longitudinal accelerating mode of a dielectric-lined waveguide structure for collinear phase-velocity-matched THz-electron interaction.

17:15 Mo-PM2-3-3
Generation Of A Few Cycle Terahertz Pulse In Aperiodically Poled Lithium Niobate By Sequence Of Pump Pulses
Yuri Avetisyan¹; Ruben Miroyan¹; Apet Barsegyan²; Masayoshi Tonouchi^3
1Yerevan State University, Armenia; ²Integra Technologies, United States; ³Osaka University, Japan

It is shown that chirped aperiodically poled lithium niobate crystal is capable to generate powerful THz pulses with controllable number of THz field oscillations (from nearly single- to multi-cycles), when it is pumped by sequence of femtosecond laser pulses with chirped delays between adjacent pulses. The peak electric field strength of about 0.3 MV/cm (for non-focused THz beam) is predicted if intensity of each pump pulse in the sequence is 20 GW/cm2.

17:30 Mo-PM2-3-4
Frequency-and-polarization-controllable High-power THz Wave Generation Using Organic Nonlinear Optical Crystal
Isao Yoshimine; Masatsugu Yamashita; Hiromichi Hoshina; Mikiko Saito; Hiroaki Minamide; Chiko Otani
RIKEN Center for Advanced Photonics, Japan

Arbitrary control of high-power THz polarization and frequency is studied by the numerical calculation based on the coupled wave approach. THz wave generation using organic crystals via optical rectification provides high conversion efficiency. To avoid the limitation of the generated THz field direction which comes from their optical anisotropy, we propose the synthesis of THz wave generated from two crystals whose optical axis are orthogonal each other. By the calculation, the linearly and circularly polarized THz wave generation by changing the time delay of two pump pulses is demonstrated.

17:45 Mo-PM2-3-5
Exceptionally High THz Energy Densities Generated From Organic Crystals Pumped With Mid- Infrared Pulses
Claudia Gollner¹; Edgar Kaksis¹; Corinne Brodeur²; Valentina Shumakova¹; Andrius Baltuska¹; Audrius Pugzlys¹; Mostafa Shalaby^2
1Photonics Institute, TU Wien, Austria; ²Swiss Terahertz Research-Zurich, Switzerland

We investigate THz generation in organic crystals (DAST and DSTMS) by optical rectification of intense Mid-Infrared pulses. The broadband spectrum exceeds several octaves when pumped by 100 fs, 3.9 μm pulses. We report on an extraordinarily high THz energy density and crystal damage threshold > 120 mJ/cm2.

18:00 Mo-PM2-3-6
Towards MJ-level Ultrashort Terahertz Generated By Optical Rectification With A Compact Terawatt Laser
Antoine Courjaud; Jean-Gabriel Brisset; Pierre Sevillano; Emilien Gontier
Amplitude Systemes, France

We report on the development of a compact diode-pumped Terawatt laser for generation of intense Terahertz pulses by optical rectification in LiNbO3. Using a 15mJ compact ultrafast laser already allowed to demonstrate 150µJ Terahertz, with 0,36% conversion efficiency. We report on a laser delivering 250mJ at 50Hz repetition rate and 480fs pulse duration, holding the potential to generate 1mJ-level Terahertz ultrashort in an equivalent setup.

16:30-18:15 - Mo-PM2-4 - 2D Materials 2 - Room 162

Chairperson: Renbin Zhong

16:30 Mo-PM2-4-1

Cavity-mediated Bound Excitons
Erika Cortese¹; Linh Ngoc Tran²; Jean-Michel Manceau³; Giorgio Biasiol⁴; Iacopo Carusotto⁵; Raffaele Colombelli⁶; Simone De Liberato^1
1University of Southampton, Department of Physics and Astronomy,United Kingdom; ²Universite Paris-Sud, Centre de Nanosciences et de Nanotechnologies, C2N-Orsay, France; ³Univ. Paris-Sud, Centre de Nanosciences et de Nanotechnologies, CNRS UMR 9001,C2N-Orsay, France; ⁴Laboratorio TASC, CNR-IOM, Italy; ⁵Universita di Trento, INO-CNR BEC Center and Dipartimento di Fisica, Italy; ⁶Univ. Paris-Sud, Centre de Nanosciences et de Nanotechnologies,CNR, C2N-Orsay, France

We experimentally demonstrate the existence of bound excitonic resonances in doped quantum wells whose electron and hole are bind by the exchange of virtual cavity photons. The theory predicts that above a certain coupling threshold a novel discrete resonance appears below the ionisation edge. In our case, the ionisation edge corresponds to the onset of the continuum above the QW barriers. This resonance describes a polaritonic excitation: part-photon and part-bound exciton. Using a sample consisting of 13 GaAs/AlGaAs n+-doped semiconductor QWs embedded in a metal / active region / metal grating cavity, we were then able to experimentally observe such a discrete resonance. We thus provided a first demonstration of the existence of a bound state of two charged particles kept together not by Coulomb interaction but by the exchange of virtual cavity photons.

17:00 Mo-PM2-4-2
The Upper Branch Broadening In Ultrastrongly Coupled THz Landau Polaritons
Shima Rajabali; Giacomo Scalari; Janine Keller; Mattias Beck; Jerome Faist
ETH Zurich, Switzerland

We present our investigation on ultrastrong coupling of the Landau level transitions in a two dimensional electron gas to complementary split ring resonator arrays, as a terahertz metasurface. To achieve a higher coupling rate, the capacitive gap of the resonator is reduced systematically. This increment in the coupling rate is expected due to the enhanced vacuum field fluctuations in a smaller volume mode. However, our results indicate that the gap size reduction introduces a broadening in the upper polariton branch below a certain gap width.

17:15 Mo-PM2-4-3
A New Tunable Topological Platform With Terahertz Band Gap: Pb1-xSnxSe
Gauthier Krizman¹; Badih Assaf²; Günther Bauer³; Gunther Springholz³; Robson Ferreira¹; Gérald Bastard¹; Louis-Anne de Vaulchier¹; Yves Guldner^1
1Ecole Normale Supérieure, France; ²University of Notre Dame, United States; ³Johannes Kepler Universität, Austria

In topological insulator thin films, new states of matter can be generated by hybridizing the massless Dirac states that occur at the topological insulator surface. In this work, we experimentally introduce a platform where this hybridization can be continuously tuned: the PbSnSe topological superlattice. Using magnetooptical transmission spectroscopy on high quality molecular beam epitaxy grown PbSnSe/ PbEuSe superlattices, we demonstrate that the energy gap emerging from this hybridization can be tuned with temperature from 1 to 10 THz. The engineering of topological states is a promising road to achieve photodetection and/or photoemission in the terahertz range.

17:30 Mo-PM2-4-4
Control Of Terahertz Nonlinearity In Graphene By Gating
Hassan A. Hafez Eid¹; Klaas-Jan Tielrooij²; Mischa Bonn³; Dmitry Turchinovich^1
1University of Bielefeld, Fakultät für Physik, Germany; ²Catalan Institute of Nanoscience and Nanotechnology, Spain; ³Max Planck Institute for Polymer Research, Germany

We study the dependence of the terahertz (THz) nonlinearity of graphene and its temporal dynamics on the free carrier concentration by THz-pump/THz-probe spectroscopy of a gated graphene at room temperature. The strong THz nonlinearity is attributed to electron heating by the driving THz field and shows a drastic dependence on the background electron concentration, demonstrating a wide-range tunability of the THz nonlinearity of graphene.

17:45 Mo-PM2-4-5
Nonlocal Photoresponse In Epitaxial Hg1-xCdxTe Films With The Inverted Band Structure
Aleksei Kazakov¹; Alexandra Galeeva¹; Alexey Artamkin¹; Sergey Dvoretskiy²; Nikolay Mikhailov²; Mikhail Bannikov³; Sergey Danilov⁴; Liudmila Ryabova⁵; Dmitry Khokhlov^1
1M.V. Lomonosov Moscow State Univ., Faculty of Physics, Russian Federation; ²Rzhanov Institute of Semiconductor Physics, Russian Federation; ³P.N. Lebedev Physical Institute, Russian Federation; ⁴Regensburg University, Germany; ⁵M.V. Lomonosov Moscow State University, Faculty of Chemistry, Russian Federation
We present our results on terahertz photoconductivity studied in Hg1-xCdxTe epitaxial films with the inverted energy spectrum (x<~0.16) in the nonlocal (H-bar type) geometry. We show that the terahertz photoresponse demonstrates nonlocality and asymmetry in magnetic field. We discuss the results in terms of a qualitative model that takes into account coexistence of the bulk transport and boundary conductive channels.

18:00 Mo-PM2-4-6
Hot Carrier Recombination Close To The Dirac Point In Graphene-hBN Van Der Waals Heterostructures
Panhui Huang; Elisa Riccardi; Federico Valmorra; Jérôme Tignon; Sukhdeep Dhillon; Bernard Plaçais; Robson Ferreira; Juliette Mangeney
Ecole Normale superieure, France

We investigate the photoconductive regime in graphene-hBN heterostructures close to the Dirac point. We demonstrate recombination lifetimes of non-equilibrium carriers in excess of 30 ps under continuous mid-infrared illumination (i.e. with photon energy below optical phonon energy in graphene). We also demonstrate the onset of an effective recombination channel relying on electron-hyperbolic phonon coupling by increasing bias. This study opens interesting perspectives to exploit graphene-hBN van der Waals heterostructures with long carrier lifetimes for THz lasing and highly sensitive THz photodetection. Our work also paves the way to develop graphene-based sources for phonon polariton optics.

16:30-18:15 - Mo-PM2-5 - Material 1 - Room 151

Chairperson: Adrien Dobroiu

16:30 Mo-PM2-5-1
Optoelectronic Properties Of Tin-Based Hybrid Metal Halide Perovskite Thin Films For Photovoltaics
Rebecca Milot¹; Michael Johnston²; Laura Herz^2
1The University of Warwick, Department of Physics, United Kingdom; ²University of Oxford, Clarendon Laboratory, UK
Due to their exceptional optoelectronic properties, hybrid metal halide perovskites thin films have shown extraordinary success as active layers in solar cells. One potential drawback of hybrid perovskites, however, is that the highest performing devices are currently based around toxic, lead-containing materials. Although tin is a promising replacement for lead, p-doping in tin-based materials has prevented them from achieving the efficiencies of their lead-based analogues. Using optical-pump/THz-probe spectroscopy and THz time-domain spectroscopy, we compare the intrinsic and extrinsic optoelectronic properties formamidinium tin triiodide thin films and comment on the fundamental limits to charge transport.

17:00 Mo-PM2-5 -2
Improved Terahertz Effective Media Models For Mixtures Of Polar Liquids
Juin W. Zhou; M. Hassan Arbab
State University of New York at Stony Brook, United States

We present two improved mixed media models for solutions of polar liquids in the THz regime. Simple effective media models do not consider intermolecular interactions or hydrogen bond network distributions in polar liquid solutions, and therefore yield inaccurate estimates of the effective dielectric functions. We present two new models: a volumetric modification to the Bruggeman equation and an effective time constant calculation in Debye-like relaxations. Furthermore, we will discuss the limitations of each model in predicting the dielectric functions.

17:15 Mo-PM2-5 -3
Investigation Of Laser-Patterned Silicon Transmittance In The Frequency Range Of 0.1-4.7 THz
Evaldas Svirplys¹; Simonas Indrisiūnas²; Heiko Richter³; Andrzej Urbanowicz⁴; Linas Minkevicius¹; Till Hagelschuer³; Gediminas Raciukaitis²; Heinz-Wilhelm Hubers³; Irmantas Kasalynas^1
1Center for Physical Sciences and Technology, Terahertz Photonics Laboratory, Lithuania; ²Center for Physical Sciences and Technology, Laser Microfabrication Laboratory, Lithuania; ³German Aerospace Center, Institute of Optical Sensor Systems, Germany; ⁴Center for Physical Sciences and Technology, Laboratory of Ultrafast Optoelectronics, Lithuania
The dependence of THz transmittance on the surface roughness of differently laser-patterned silicon was investigated in the frequency range of 0.1-4.7 THz. The scattering of THz waves on rough silicon surface was found as the main mechanism that determines optical losses. The impact of silicon processing in ambient air and argon-rich environments on the THz absorption losses was also observed.

17:30 Mo-PM2-5 -4
Retrieving Permittivity Model Parameters For Polar Liquids And Multilayer Systems Through THz-TDS Time-trace Data Analysis
Melanie Lavancier; Sergey Mitryukovskiy; Nabil Vindas; Jean-François Lampin; Romain Peretti
IEMN, CNRS UMR 8520, France

We present new features of the Fit@TDS software for the analysis of polar liquids and multilayer systems. We also show that the modeling of the absorption coefficient of polar liquids can be improved above 2.5THz. Hence, this software will enable us to retrieve the parameters of the models depicting polar liquids. It will help to analyze and compare charges motions, playing an important role in biology and chemistry with such effects as protein solvation. Finally, the implementation of a scattering model will improve the accuracy of the results. These features will be illustrated with THz-TDS experiments on biological samples (sugars, amino acids, enzymes, emulsions).

17:45 Mo-PM2-5 -5
Observation Of Phase Change Of Methane Hydrate Using THz Waves
Keisuke Matsumura; Kei Takeya; Kodo Kawase
Nagoya University, Japan

We observe a phase change of methane hydrate, which is expected to be a new energy resource, using THz Time-Domain Spectroscopy (THz-TDS). In the temperature zone where methane hydrate should be decomposed, an increase in absorption and a shift in time-domain waveform are observed, which seems to indicate that the sample is mutated.

18:00 Mo-PM2-5 -6
Redox Chemistry In Eumelanin
Zarina Gagkaeva¹; Konstantin Motovilov²; Vadim Grinenko³; Maxim Savinov⁴; Lenar Kadyrov²; Alexei Pronin⁵; Zakhar Bedran²; Elena Zhukova²; Bernard Mostert⁶; Boris Gorshunov^2
1Moscow Institute of Physics and Technology, Russian Federation; ²MIPT, Russian Federation; ³Institute for Solid State and Materials Physics, Germany; ⁴Institute of Physics of the Czech Academy of Sciences, Czech Republic; ⁵Prokhorov General Physics Institute of the Russian Academy of Sciences, Russian Federation; ⁶Department of Chemistry, Swansea University, United Kingdom

Eumelanin is a perspective conductive biomolecular material, which has already been used for making various bioelectronic devices ranging from transistors to batteries. It is known that its conductivity mechanisms are governed by a redox comproportionation reaction. However, most studies devoted to the redox chemistry of eumelanin lack the data on the temperature behavior of its properties. We use broadband dielectric spectroscopy and heat capacity measurements to study the influence of hydration and temperature on eumelanin's conductivity.

16:30-18:15 - Mo-PM2-6 - Instrum. Biology - Room 101

Chairperson: Gun-Sik Park

16:30 Mo-PM2-6-1
An Ultrasensitive Terahertz Microfluidic Chip Based On Fano Resonance Of A Few Arrays Of Meta-atoms
Kazunori Serita; Hironaru Murakami; Iwao Kawayama; Masayoshi Tonouchi
Osaka University, Japan

We present a nonlinear optical crystal-based terahertz (THz)-microfluidic chip with a few arrays of asymmetric meta-atoms for the measurements of trace amount of solutions. A near-field THz emission source that is locally generated in the process of optical rectification at the irradiation spots of fs laser beams induces a high-Q Fano resonance and modifies the resonance frequency of the meta-atoms when the channel between meta-atoms is filled with solutions with different concentrations. Using this chip, we successfully detected attomole order of solute in a less than 100 pL volume of the solution.

17:00 Mo-PM2-6-2
An Optical Instrument For The Submillimeter Spectroscopy Of The Volatile Metabolome
François Bondu¹; Goulc'hen Loas¹; Ludovic Frein¹; Cyril Hamel¹; Anthony Carré¹; Virginie Daburon²; Françoise Binet²; Guillaume Ducournau³; Jean-François Lampin^3
1CNRS, Univ Rennes, Institut FOTON UMR6082, France; ²CNRS, Univ Rennes, ECOBIO UMR 6553, France; ³CNRS, Université Lille 1, IEMN UMR 8520, France

We are designing and realizing an instrument for the spectroscopy of the volatile metabolome of the soil microorganisms. The use of optical telecommunication elements makes it possible to realize a compact source with a wide range of accessible frequencies (100 GHz - 1 THz range; 3-33 cm?¹) with an accuracy of 10? Hz (3.10?? cm?¹), as well as a low bandwidth detection system. The instrument will discriminate among complex polar molecules. We report on the preliminary performances of parts of the source system.

17:15 Mo-PM2-6-3
Towards Broadband THz Spectroscopy And Analysis Of Sub-wavelength-size Biological Samples
Sergey Mitryukovskiy; Mélanie Lavancier; Flavie Braud; Yue Bai; Emmanuel Dubois; Jean-François Lampin; Romain Peretti
IEMN CNRS/Université de Lille, France

We report on our recent progress toward bio-photonic applications of terahertz time-domain spectroscopy. First, we developed a technique for the confinement of broadband terahertz pulses to a sub-wavelength-volume, and will present its applications to study biological samples. Second, we will discuss the analysis of terahertz time-trace data from bio-samples using our Fit@TDS software based on the time-domain optimization algorithm that enables direct fitting of sample parameters. The combination of these (the experimental and the modelling) techniques is a robust tool for terahertz bio-photonics.

17:30 Mo-PM2-6-4
Technique For Recording THz Response From Bio-Tissue
Maksim Fomin¹; Konstantin Taranets¹; Nikolay Bagraev²; Leonid Klyachkin²; Vladislav Odintsov³; Vyacheslav Bazarbaev^4
1Peter the Great St.Petersburg Polytechnic University (SPbPU), Russian Federation; ²Ioffe Institute, Russian Federation; ³St Petersburg Clinical hospital of RAS, Russian Federation; ⁴ANO CPE "Institute of Mammology", Russian Federation

The results obtained show the promise of further research in the field of recording THz response from biological tissue with the SNS balance device.

17:45 Mo-PM2-6-5
Quantification Of DsDNA Functionalization Efficiency In THz Biosensors
Christian Weisenstein¹; Merle Schmeck¹; Dominik Schaar²; Anna Katharina Wigger¹; Anja Bosserhoff²; Peter Haring Bolívar^1
1University of Siegen - High Frequency and Quantum Electronics, Germany; ²Friedrich-Alexander-University Erlangen-Nürnberg, Germany

In the past, THz bioanalytical techniques have been proven to be viable tools for label-free detection of biomolecules. However, significant improvements in the detection limit are needed to apply THz biosensors in biomedical diagnosis. To determine detection limits of the biosensor and the absolute amount of sample volume, quantitative measurements are required. We present label-free THz sensing of dsDNA and implement an approach based on reference investigations to quantify the dsDNA functionalization density. Defined functionalization densities are vital to maximize the adsorption of a dsDNA groove-binding protein, which acts as a tumor marker for malignant melanoma.

18:00 Mo-PM2-6-6
Pressure Controlled In Vivo THz Measurements Of Skin: Monitoring The Effects Of Moisturizers
Hannah Lindley¹; A. I. Hernandez-Serrano¹; Qiushuo Sun²; Jiarui Wang²; Emma Pickwell-MacPherson^1
1University of Warwick, Dpt of Physics, United Kingdom; ²Chinese University of Hong Kong, Dpt of Electronic Engineering, Hong Kong

Pressure is a variable which must be controlled during in vivo skin measurements if comparisons between subjects and measurements are to be obtained. We have built a device to indicate (and record) if the contact pressure between the skin and the imaging window is within the desired range at the time of measurement. Using this device, terahertz (THz) measurements of skin before and after the application of a commercial skin-care product were taken. Significant changes in the THz skin properties were observed, which cannot therefore be attributed to varying contact pressure. These results demonstrate that with a rigorous protocol THz imaging has the potential to be used for testing new skin products and quantifying their effects on the skin and how long these last.

18:15-19:30 - Poster session - Mo-Po 1 - Room 8

Mo-Po1-1
Scattering Of THz Radiation By Spherical MWCNTs Aerogel In State Of Acoustic Levitation
Alexander Badin¹; Igor Dorofeev¹; Grigorii Dunaevskii¹; Valentin Suslyaev¹; Dmitriy Bodazhkov¹; Kseniya Simonova¹; Sergey Moseenkov²; Vladimir Kuznetsov^2
1National Research Tomsk State University, Russian Federation; ²Boreskov Institute of Catalysis SB RAS, Russian Federation

Recently created aerogel with multi-walled carbon nanotubes (MWCNTs) finds more and more new applications due to its unique properties: optimal weight and dimensional parameters, strength, and electrical conductivity. One of MWCNTs aerogel application may be used as a probe fixed in an acoustic standing wave in a tract of a terahertz spectrometer. Therefore, it is of interest to carry out research of the THz radiation scattering by aerogel. The transmission coefficient measurements at various positions of the aerogel in the beam using a BWO spectrometer at the frequency range 63-124 GHz were made. For levitation of aerogel we use acoustic levitation cell based on local transducers. Average diameter of MWCNTs aerogel was 2.7 mm. The calculation of extinction of ideal conductive balls with a diameter of 2.75 mm (MWCNTs aerogel with a specific conductivity of 103 Sm/m and ideally conductive) was carried out.

Mo-Po1-2
FT-ESR Measurements On BDPA By Pulsed ESR Using A Gyrotron As High-power Millimeter Wave Source
Seitaro Mitsudo; Kaishi Kono; Kazuki Dono; Kanata Hayashi; Yuya Ishikawa; Yutaka Fujii
Research Center for Development of Far-Infrared Region, University of Fukui, Japan

Pulsed ESR spectroscopy system was developed using the high-power millimeter wave of gyrotron. The FID signal of stable radicals of BDPA diluted with polystyrene was successfully observed by the quadrature detection method. By Fourier transforming of these FID signals, high resolution FT-ESR spectrum of BDPA was successfully obtained.

Mo-Po1-3
The Fundamental Terahertz Mode Of L-Alanine: Strong Narrowing, Greater Symmetry And Small And Non-Uniform Shift As Temperature Is Reduced
Thomas Sanders; Jackson Allen; Matthew Large; Josip Horvat; Roger Lewis
University of Wollonogong, Australia

We have measured the spectrum of L-alanine in the terahertz region over a wide temperature range, from 15 to 300 K. At the lowest temperature, the fundamental line is very sharp, of intrinsic width 0.02 THz (0.8 cm-1). As temperature increases, the line broadens, undergoes a non-uniform red shift, becomes more asymmetrical and decreases in oscillator strength.

Mo-Po1-4
Density Of State Of Low-frequency Intramolecular Vibrations For Stiff And Flexible Molecules At Solid Phase
Feng Zhang¹; Hong-Wei Wang²; Keisuke Tominaga¹; Michitoshi Hayashi²; Tetsuo Sasaki^3
1Molecular Photoscience Research Center, Kobe University, Japan; ²Center for Condensed Matter Sciences, National Taiwan University, Taiwan; ³Research Institute of Electronics, Shizuoka University, Japan

Densities of state (DOS) of intramolecular vibrations in optical phonon modes have been quantitatively studied for three oligoglycines. Polycyclic aromatic chain molecules have been used as references. We found that the more flexible backbones of oligoglycines lead to drastically faster growth of intramolecular vibrations with the increase of frequency than the stiffer backbones of polycyclic aromatics do.

Mo-Po1-5
Ionic Current In Superionic Conductor Na+ Beta-Alumina Induced By Terahertz Electric Fields
Yasuo Minami¹; Benjamin Ofori-Okai²; Prasahnt Sivarajah³; Ikufumi Katayama⁴; Jun Takeda⁴; Keith Nelson³; Tohru Suemoto^5
1Tokushima University, Japan; ²SLAC National Accelerator Laboratory, United States; ³Massachusetts Institute of Technology, United States; ⁴Yokohama National University, Japan; ⁵Toyota Physical and Chemical Research Institute, Japan

We demonstrate that intense terahertz (THz) electric-field transients can manipulate the motion of ions in an ionic conductor. The cations trapped in local potential minima are accelerated by single-cycle THz pulses leading to a macroscopic current flow.

Mo-Po1-6
Response Of Strongly Nonequilibrium Plasma Created By High Power Short UV Laser Pulse In Rare Gases To THz Frequency Band Emission
Alexander Popov; Anna Bogatskaya; Ekaterina Volkova
Moscow State University, Russian Federation

The response of plasma created by multiphoton gas ionization in an intense UV laser pulse to the terahertz frequency band radiation is studied. Analysis is based on the Boltzmann equation for the temporal behavior of the electron velocity distribution function (EVDF) in an arbitrary external electric field and allows to take into account both temporal retardation of the EVDF evolution with respect to the external electric field and the effect of the relaxation of the strongly nonequilibrium EVDF due to elastic electron - atomic collisions. The suggested theory enables to properly describe propagation of ultra-short THz pulses in laser plasma waveguides.

Mo-Po1-7
Dynamics Of A Sub-terahertz Discharge In The Heavy Noble Gases Produced By A High-density Radiation Field
Alexander Sidorov; Sergey Razin; Alexey Veselov; Mikhail Victorov; Alexander Vodopyanov; Mikhail Morozkin; Mikhail Proyavin; Mikhail Glyavin
Institute of Applied Physics of the Russian Academy of Sciences (IAP RAS), Russian Federation

Results of the experimental investigation of the discharge front propagation in the beams of powerful sub-terahertz radiation are presented. The front propagation velocity is measured in the wide range of the gas (argon, krypton) pressure (0.1 -- 1 atm). It is demonstrated that the discharge front runs against the incident sub-terahertz radiation beam into the region with the electric field value well below the threshold. Discharge propagation slowing down in correspondence with the electric field strength decrease. Characteristic propagation velocity value is in the range of 10^5 -- 10^6 cm/s.

Mo-Po1-8
A Coherent Smith-Purcell Radiation Source: Design Considerations For A High Power, Tunable Source Of Terahertz Radiation
Huibo Zhang; Ivan Konoplev; George Doucas
John Adams Institute for Accelerator Science, Department of Physics, University of Oxford, United Kingdom

The concept of coherent terahertz (THz) tunable Smith-Purcell radiation source driven by the microbunched electron beam is presented. Studies were performed using numerical and analytical approaches to investigate the radiation generated by electron microbunches. It is demonstrated that the capability of manipulating the microbunching of electron beams results in the possibility to control both the radiation power and the frequency of coherent Smith-Purcell radiation (cSPr). Numerical results were compared with analytical calculations and there is a good agreement between them. These proof of concept studies demonstrate the possibility of designing a high power, broadly tunable THz radiation source.

Mo-Po1-9
Modulation Of Terahertz Wave Based On A Preionized Plasma
Liangliang Zhang¹; Tong Wu²; Hang Zhao²; Rui Zhang³; Cunlin Zhang¹; Yuejin Zhao^2
1Capital Normal University, Department of Physics, China; ²Beijing Institute of Technology, China; ³Shenzhen Institutes of Advanced Technology, Chinese Academy of Sciences, China

We demonstrate the modulation of terahertz wave generation from two-color femtosecond laser filament on the basis of a preionized air plasma background created by a modulation pulse using an orthogonal pumping geometry. This is achieved by adjusting and optimizing the phase difference between the two-color laser fields, which is introduced when the two-color fields goes through the preionized air plasma. The results are reasonably coincident with our theoretical simulation based on the plasma photocurrent model. Our results can contribute to the further understanding of the generation mechanism of terahertz wave, enhance the generation efficiency and expand the practical application of terahertz wave.

Mo-Po1-10
3-D Calculations Of Terahertz Generation In The Tilted-pulse-front Scheme
Lu Wang; Franz kaertner
DESY, Germany

The tilted-pulse-front setup utilizing a diffraction grating is one of the most successful methods to generate single- to few-cycle terahertz pulses. However, the generated terahertz pulses have a large spatial inhomogeneity, due to the noncollinear phase matching condition and the asymmetry of the prism-shaped nonlinear crystal geometry, especially when pushing for high optical-to-terahertz conversion efficiency. Thus, a 3D+1 numerical model is necessary for investigating the terahertz generation problem in the tilted-pulse-front scheme. In this article, we compare the differences of the 1D+1, 2D+1 and 3D+1 numerical models. The simulation results suggest a strong spatial dependence on the generated terahertz electric field. The single-cycle pulses are only generated at the neighborhood around the apex of the prism. This strong spatial dependence must be accounted for when using the terahertz pulses for strong-field physics and carrier-envelope-phase sensitive experiments

Mo-Po1-11
High Cubic Nonlinearity Of Liquids In The Broadband THz Spectral Range
Maria Zhukova¹; Maksim Melnik¹; Anton Tcypkin¹; Irina Vorontsova¹; Sergey Putilin¹; Sergei Kozlov¹; Xi-Cheng Zhang^2
1ITMO University, Russian Federation; ²University of Rochester, United States

Here we report the direct measurement of the nonlinear refractive index coefficient of liquids by using the Z-scan method with broadband pulsed THz beam. The results fit with conventional Z-scan analytics well. We estimate the nonlinear refractive index coefficient n2 of liquids through the use of the theoretical treatment that takes the ionic vibrational contribution into account. This estimation correlates with experimental data obtained.

Mo-Po1-12
Intersubband Terahertz Emission From Coupled GaAs/AlGaAs Double Quantum Wells Under Interband Photoexcitation
Alexander Andrianov; Alexey Zakhar'in
Ioffe Institute, Russian Federation

Terahertz range photoluminescence from specially designed structures with tunnel coupled double quantum wells under interband optical excitation has been investigated. A series of narrow emission lines were observed and interpreted as intersubband radiative transitions between electron quantum confinement levels.

Mo-Po1-13
Transformation Of The Terahertz Polarization During Three-Wave Joint Propagation In Liquid Nitrogen
Petr Solyankin¹; Alexander Shkurinov²; Nikolai Kuzechkin¹; Alexei Balakin²; Vladimir Makarov^2
1ILIT RAS - Branch of the FSRC «Crystallography and Photonics» RAS, Russian Federation; ²Lomonosov Moscow State University, Russian Federation

In this work we experimentally and theoretically investigate the mutual action of three copropagating waves in isotropic nonlinear medium (liquid nitrogen). Two waves are the first and the second harmonic of the Ti:Sa laser system, and the third one is the terahertz wave generated in the spark of optical breakdown of air. After propagation through liquid nitrogen the change in terahertz polarization state is observed. We attribute this phenomenon to the nonlinear "Terhune-like" mutual rotation of the main axis of a polarization ellipse of terahertz radiation.

Mo-Po1-14
Optimization Of Terahertz Source Via An Ambient Air-Based Multi-Color Photoionization
Po-Hsun Wu¹; Chan-Shan Yang²; Po-Hsun Chen³; Wei-Che Hu³; Hai-Wei Du⁴; Xiao-Yu Peng⁵; Ci-Ling Pan^1
1National Tsing Hua University, Taiwan; ²Institute of Electro-Optical Science and Technology, National Taiwan Normal University, Taiwan; ³National Tsing Hua University, Taiwan; ⁴Nanchang Hangkong University, China; ⁵Center for Terahertz Technology Research, Chongqing Institute of Green and Intelligent Technology, China

By applying the well-known transient current model, theoretically investigating terahertz (THz) emission from gas plasma induced by multi-color femtosecond laser pulses has been developed in this work. Instead of static tunneling ionization model, we adopted Ammosov-Delone-Krainov (ADK) tunneling ionization model to calculate the tunneling ionization rate. In three-color pumping schemes, the optimal power ratio tends to require a larger amount of fundamental field with the increment of total pump power. The optimal relative phases for the 2nd harmonic and 3rd harmonic field are 0.5πand π , respectively.

Mo-Po1-15
On The Prospects For The Study Of A Point Discharge Sustained By A Terahertz Free Electron Laser Radiation In An Inhomogeneous Gas Flow
Alexander Vodopyanov¹; Alexander Sidorov¹; Alexey Veselov¹; Vitaly Kubarev²; Oleg Shevchenko²; Yaroslav Gorbachev^2
1Institute of Applied Physics of the Russian Academy of Sciences (IAP RAS), Russian Federation; ²Budker Institute of Nuclear Physics RAS, Russian Federation

It is proposed to use high-power radiation from a terahertz free electron laser to create a localized (point-like) discharge in an inhomogeneous gas flow. Plasma parameters that can be achieved in such a system open up prospects for creating an effective point-like source of extreme ultraviolet light for the next-generation projection lithography.

Mo-Po1-16
High Conversion Efficiency In The System "Nonlinear-Optical Crystal Partially Filling The Cross Section Of A Rectangular Waveguide"
Anahit Nikoghosyan
Yerevan State University, Armenia

It is shown that terahertz radiation (0.1-3 THz) can be effectively generated via optical rectification of femtosecond laser pulses in a system of a "nonlinear-optical crystal partially filling the cross section of a rectangular metal waveguide". The numerical calculations for the phase-matching in LiNbO3, ZnTe, DAST and GaSe nonlinear optical crystals have been performed. The influence of THz radiation absorption on the efficiency of generation of coherent THz radiation in the system has been investigated.

Mo-Po1-17
Strong Terahertz Electromagnetic Wave Generation Due To Intense Laserplasma Interaction Mechanisms
Andrey Kuratov¹; Andrey Brantov²; Yuriy Aliev²; Valery Bychenkov^2
1Center of Fundamental and Applied Research, VNIIA, Russian Federation; ²Lebedev Physical Institute RAS, Russian Federation

Strong THz waves have a wide range of applications. Laser -- plasma interaction has advantages over other methods for high power THz generation. We report on our theoretical and numerical investigations of three different mechanisms of THz radiation generation from the laser-plasma sources. We have identified the most effective mechanism of THz pulse generation and quantitatively characterized its properties.

Mo-Po1-18
Terahertz Wave Generation Using Single Or Few-Cycle Laser Pulses In A Gaseous Medium
Rajaram Shrestha; Kyung Taec Kim
Gwangju Institute of Science and Technology, Democratic People's Republic of Korea

We perform theoretical calculations to demonstrate that single or few-cycle laser pulses can generate an intense terahertz (THz) emission by a directional current. The THz wave is strongest at the carrier-envelope phase (CEP) of 90 deg. The strength of the THz wave increases as the pulse duration decreases. The results clearly show that the THz wave is maximized when the directional current is maximized.

Mo-Po1-19
Nonlinearity In Indium Phosphide Using THz Radiation
Rakesh Kumar Vaddapally¹; Chandra vardhan Kotyada¹; Kamalesh Jana¹; Amit D Lad¹; Yash Mukesh Ved¹; Shriganesh Prabhu¹; Gottfried H Döhler²; Ravindra Kumar Gattamraju^1
1Tata Institute of Fundamental Research, India; ²Max Planck Institute for the Science of Light, Germany

Broad band Terahertz(THz) radiation has been used to study the non-linearity in semiconductor materials. The broad band source has been generated using the two color mixing technique from a 20 TW class system. The energy and intensity of the broadband terahertz source which is of the order of microjoules and MV/cm is intense enough to induce non-linearity in the semiconductor. The photon energy of the THz radiation is of the order of meV which is much less than the band gap of the semiconductor materials. Still THz radiation is able to induce nonlinear nature in Indium Phosphide semiconductor. The free carriers are scattered from lowest inter-valley of the semiconductor to the next highest inter-valley of the semiconductor in the conduction band leading to the reduction of overall conductivity of the semiconductor. Thus causing high transmission of THz showing non-linearity in the semiconductor.

Mo-Po1-20
Terahertz Generation By Two-color Laser Filamentation
Sarath Maratha Palli¹; Philipp Wustelt¹; Slawomir Skruszewicz¹; Gerhard G Paulus¹; Sergey Popruzhenko²; Amrutha Gopal^1
1Institut für Optik und Quantenelektronik, Germany; ²Prokhorov General Physics Institute, Prokhorov General Physics Institute, 38 Vavilov str., Russian Federation

Generation of broadband terahertz radiation in air by ionization using two-color femtosecond laser pulses is investigated. Terahertz pulse energy is enhanced by varying the polarization of the laser pulses. We also investigated the influence of phase shift between the femtosecond pulses on the emitted terahertz energy.

Mo-Po1-21
Second Optical Harmonic Generation From Interfaces Of Isotropic Materials In Strong Terahertz Field: Surface Vs Bulk Contributions
Sergey Bodrov¹; Michael Emelin²; Yuri Sergeev²; Alexey Korytin²; Michael Ryabikin²; Andrey Stepanov^2
1University of Nizhny Novgorod, Russian Federation; ²Institute of Applied Physics of the Russian Academy of Sciences, Russian Federation

Second optical harmonic generation by nonlinear interaction of femtosecond laser and terahertz pulses in a slab of fused quartz was investigated. It was shown that the second harmonic signal rises only near the slab surfaces and not from the bulk of the fused quartz. The theory of THz induced second optical harmonic in transparent material including dispersion of the optical radiation as well as velocity mismatch of THz and optical pulse was developed. The theory agrees well with experiment.

Mo-Po1-22
THz Generation In Laser Filament Under Electric Field Conditions
Valery Losev; Dmitrii Lubenko; Vladimir Prokopev; Sergey Alekseev; Mikhail Ivanov
IHCE SB RAS, IHCE SB RAS, Russian Federation

We present experimental results of generation THz range radiation in a laser plasma. Comparison of one and two-color optical pumping schemes are presented. We report about dependence THz radiation energy from electrical field application point to filament. The maximum generation efficiency is observed when an electric field is applied to geometrical focus point (laser filament is formed from geometrical focus point towards the laser source). The mechanisms of this effect are discussed.

Mo-Po1-23
Competition Between Positive And Negative Terahertz Photoconductivity In Variable Thickness Hg1-xCdxTe Epitaxial Layers
Alexandra Galeeva¹; Alexey Artamkin¹; Alexey Kazakov¹; Mikhail Bannikov²; Anton Ikonnikov¹; Sergey Dvoretskiy³; Nikolay Mikhailov³; Sergey Danilov⁴; Ludmila Ryabova¹; Dmitry Khokhlov^1
1M.V. Lomonosov Moscow State University, Russian Federation; ²P.N. Lebedev Physical Institute, Russian Federation; ³Rzhanov Institute of Semiconductor Physics, Russian Federation; ⁴Regensburg University, Germany

In this work, we demonstrate that the terahertz photoconductivity in Hg1-xCdxTe epitaxial films (x = 0.13 -- 0.15) is featured by superimposed positive and negative components. The dramatic drop of the positive photoresponse as the sample thickness decreases indicates the crucial role of the bulk carrier contribution to the non-equilibrium transport. However, the photoresponse behavior observed in the magnetic field applied is an argument for an edge phototransport channel formation. We discuss the sign-alternating photoconductivity kinetics in terms of the model that takes into account both the bulk electron excitation and the surface/interface states contribution.

Mo-Po1-24
Continuous Wave Microscopy Based On Solid Immersion Lens
Yesenia Angélica García Jomaso¹; Naser Qureshi²; Calos Gerardo Treviño Palacios³; Jesús Garduño Mejía²; Rafael Izazaga Pérez^3
1Universidad Nacional Autónoma de México, Mexico; ²ICAT-UNAM, Mexico; ³INAOE, INAOE, Mexico

We describe a basic approach of transmission terahertz microscopy based on solid immersion lenses. We use a Backward Wave Oscillator (BWO) as a radiation source, a hyperemispherical silicon lens as solid immersion lens and as a detector a low power pyroelectric. The experimental results show that with this approach we can improve the terahertz spot diameter size of the system compared with a simply aspherical lens. The spot diameter at the focus of the immersion lens is about 0.34 ? at 600 GHz. This approach is extended to an interferometric system to achieve a better sensitivity of the microscope.

Mo-Po1-25
Simulation Of A THz Sheet Beam Cyclotron Resonance Staggered Double Grating Traveling Wave Tube
Yu Fan; Zhiqiang Zhang
Institute of electronics, Chinese academy of sciences, China

A Y band cyclotron resonance staggered double-grating traveling wave tube (TWT) is simulated, and a sheet beam with cyclotron electrons is applied to the TWT. Simulation result of the cyclotron resonance enhancement effect is shown. Different ratios of the transverse velocity and longitudinal velocity are compared.

Mo-Po1-26
Terahertz Time-Domain Polarimetry Of Carbon Nanomaterials
Anatoly Kvitsinskiy¹; Petr Demchenko¹; Alexander Grebenchukov¹; Egor Litvinov¹; Maxim Masyukov¹; Anton Zaitsev¹; Ilya Anoshkin¹; Anna Baldycheva²; Evgeniya Kovalska²; Anna Vozianova¹; Mikhail Khodzitsky^1
1ITMO University, Russian Federation; ²University of Exeter, United Kingdom

Terahertz time-domain spectroscopic polarimetry (THz-TDSP) method was used to study of polarization properties of a few-layer graphene (FLG) and a randomly oriented single-walled carbon nanotube (SWCNT) thin film on silicon (Si) substrates in terahertz (THz) frequency range under an external optical pumping (OP) and an external static magnetic field (MF). Frequency dependencies of azimuth and ellipticity angles of a polarization ellipse of the samples were obtained experimentally. The results confirm the fact that, based on carbon nanomaterials, it is possible to devise tunable THz polarization modulators for use in the latest security and telecommunication systems.

Mo-Po1-27
THz EMI Shielding In Graphene/PMMA Multilayers
Can Koral¹; Gianpaolo Papari²; Maria Giovanna Pastore Carbone³; Christos Pavlou³; Costas Galiotis³; Antonello Andreone^1
1INFN_National Institute of Nuclear Physics Section of Naples, Italy; ²Department of Physics, University of Naples "Federico II", Italy; ³FORTH/ICEHT Patras, Greece

The electromagnetic interference (EMI) shielding mechanisms of graphene/PMMA multilayered structures are experimentally investigated by using time domain spectroscopy (TDS) in the THz range. Stacked plates of similar thickness (~ 5μm), starting from a single layer up to 100 layers, were produced by a novel approach combining ultra-thin polymer casting and wet deposition techniques. These nano laminates show enhanced electrical conductivity (~ 100 S/cm) and superior specific shielding effectiveness (~ 2-10^4 dB cm² g^-1).

Mo-Po1-28
Tri-band Linear To Circular Polarization Converter Based On Transmissive Metasurfaces
Ayesha Kosar Fahad; CunJun Ruan; Tanveer Ul Haq; Shahid Ullah
School of Electronic and Information Engineering, Beihang University, China

Multi-band operation for terahertz wireless systems is a challenging problem. We propose a triple-band linear to circular polarization converter in the Terahertz regime using metasurfaces in transmission modes. The converter is composed of bi-layered metasurfaces separated by a dielectric spacer. Three bands (0.54-0.804, 1.904-2.476, and 2.96-3.884 THz) of linear to circular polarization conversion (LCPC) are achieved due to the superposition of the two transmitted components with a near 90Ã,° phase difference. Idea is verified by finite element method simulation and paves a way to the design of multi-band ransmissive LCPC

Mo-Po1-29
Ionic Permeability And Interfacial Doping Of Graphene On SiO2 Measured With Terahertz Photoconductivity Measurements
Hai Wang¹; Xiaoyu Jia¹; Mischa Bonn¹; Klaas-Jan Tielrooij^2
1Max Planck Institute for Polymer Research, Germany; ²Catalan Institute of Nanoscience and Nanotechnology (ICN2), Spain

Graphene has been widely used in various electrochemical applications owing to its outstanding electrical and chemical properties. The presence of electrolyte at the graphene surfaces affects graphene's electronic properties, especially its electrical conductivity. The precise mechanism underlying the graphene-electrolyte interaction has remained elusive, despite the importance of graphene for electrochemical applications. Here, we employ optical-pump THz-probe spectroscopy as a contact-free and all-optical means to investigate the impact of cations on graphene conductivity in the electrolyte. We reveal ionic permeability though graphene, resulting in an interfacial doping effect in SiO2-supported graphene.

Mo-Po1-30
Temperature Dependent Sheet Conductivity Of MoS2 Measured By Terahertz Time-Domain Spectroscopy
Tao Li; Jun Zhou; Yanshun Zheng; Zheng Zhu; Lin Zhou; Xin Rao; Jun Wang
University of Electronic Science and Technology of China, China

In this work, a typical two-dimensional (2D) material MoS2 has been measured by terahertz time-domain spectroscopy (THz-TDS), and its temperature dependent properties in the temperature range fom 120 K to 500 K have been studied. The transmittance and sheet conductivitiy of monolayer MoS2 have been obtained at different temperatures. This study is useful for the understanding of 2D materials in the THz frequency regions.

Mo-Po1-31
Transmission Properties Of Transition Metal Dichalcogenides And Modified Graphene Thin Films In Visible, NIR And THz Frequency Ranges
Maria Zhukova¹; Egor Oparin¹; Polina Shaban¹; Anton Tcypkin¹; Ben Hogan²; Evgeniya Kovalska²; Monica Craciun²; Anna Baldycheva^2
1ITMO University, Russian Federation; ²University of Exeter, United Kingdom

Here we demonstrate the transmission properties of a thin tungsten disulfide WS2 film fabricated from liquid crystal solutions in near-infrared and THz ranges. These results are compared with other transition metal dichalcogenides transferred to different substrates and unique FeCl3 intercalated graphene-based structures. The introduction of impurities, the selection of structural dimensions and the use of an appropriate substrate for modified 2D layered materials allow controlling the transmission of samples for both the terahertz and infrared ranges, which can be used for the creation of effective modulators and components for THz spectroscopy systems.

Mo-Po1-32
Strong Carrier Temperature Dependence Of Complex THz Conductivity of Photo-excited Graphene Due To Electron-phonon Coupling
Masatsugu Yamashita; Sho Ikeda; Chiko Otani
RIKEN, Japan

Ultra-broadband THz conductivities of doped monolayer graphene on PET substrate after photo-excitation at various optical pump fluence are investigated. THz conductivity corresponds to the intra-band transition of hot carriers decreases and deviates from the Drude-type frequency dependence as the pump fluence increases, indicating the broader carrier-energy distribution and energy dependent scattering. However, we found that the semi-classical Boltzmann transport theory with dominant carrier scattering mechanisms such as charged impurity and intrinsic optical phonon scattering with e-ph coupling strength from Density functional theory within GGA approximation failed to explain the hot carrier temperature dependence of THz conductivity spectra. This result suggests that the underestimation of e-ph coupling by DFT calculation and the importance of e-e interaction on the e-ph coupling

Mo-Po1-33
Intraband Ultrafast Terahertz Conductivity Dynamics In Graphene
zeyu zhang; Tingyuan Jia
Shanghai Institute of Optics and Fine Mechanics, China

Understanding the subpicosecond carrier dynamics of graphene play a crucial role in its optoelectronic allications. By using various photon energy pump, THz probe spectroscopy, the thermalization dynamics of monolayer graphene was presented. For a doped graphene, the thermal induced intraband terahertz conductivity dynamics shows typically thermal relaxation process in our experiment. The importance of the hot carrier multi-plication process of impurities scattering is discussed for graphene photodetector device applications.

Mo-Po1-34
Refractive Index Modulation Induced By High-Intensity THz Radiation
Mohammed Almassarani¹; Abel Woldegeorgis²; Takayuki Kurihara³; Amrutha Gopal^2
1Helmholtz Institute Jena, Germany; ²Institute of Optics and Quantum electronics, Germany; ³University of Konstanz, Germany

Nonlinear refractive index and absorption coefficient are measured for common semiconductor material such as silicon and organic molecule such as lactose in the terahertz (THz) spectral regime extending from 0.1 to 3 THz. THz pulses with a field strength of 440 MV/m have been employed. Transmittance and the transmitted spectra were measured using Z-scan and single shot noncollinear electro-optic pump-probe techniques. A maximum change in refractive index (Δn) of - 0.128 and +0.245 were measured in lactose and silicon, respectively.

Mo-Po1-35
THz Spatial Modulation In The Fourier Plane
Polina Stefanova; Andreas Klein; Claudio Balocco; Andrew Gallant
Durham University, Department of Engineering, United Kingdom

Application of the real-time image processing method of 4F optical systems is presented in the THz regime. Direct manipulation of the Fourier transform of an image through addressable metamaterials is to be explored, in order to achieve THz spatial modulation, beam forming and beam steering.

Mo-Po1-36
The Terahertz Near-field Response Of Graphene Layers And Graphene Structures
Valerii Trukhin¹; Ilia Mustafin¹; Sergey Lebedev¹; Anna Baldycheva^2
1Ioffe Institute, Russian Federation; ²University of Exeter, United Kingdom

We report on the experimental study of scattering and the near-field interaction of a THz electromagnetic field with graphene layers near the probe of a terahertz near-field microscope. There are resonance lines in the spectrum for a graphene monolayer-based transistor structure, which is possibly due to the strong plasmon response at terahertz frequencies and the manifestation of plasmon interference in the graphene strip.

Mo-Po1-37
Sensitivity Measurement Of Resonant-Tunneling-Diode Terahertz Detectors
Yuma Takida¹; Safumi Suzuki²; Masahiro Asada²; Hiroaki Minamide^1
1RIKEN, Japan; ²Tokyo Institute of Technology, Japan

We report on the performance characterization of resonant tunneling diode (RTD) devices as a terahertz (THz)-wave detector. The frequency-dependent sensitivity of quasi-optical RTD detectors has been calibrated by using a frequency-tunable, sub-ns pulsed THz-wave source. The 0.78-THz, slot-antenna-integrated RTD device shows the peak responsivity of 80 V/W at 0.76 THz with the full-width at half-maximum bandwidth of 70 GHz.

Mo-Po1-38
Observation Of Dirac Semi-metallic Topological State In SrIrO3 And CaIrO3 Using Terahertz Time-domain Spectroscopy
Dhanvir Rana; Santhosh Kumar K
Indian Institute of Science Education and Research (IISER) Bhopal, India

Experimental realization of quantum phases such as Dirac and Weyl semimetals, topological insulators and superconductors is an emerging subject of interest in condensed matter physics. In this talk, I will give a brief introduction to Dirac semimetals and theoretical predictions of such ground state in orthorhombic perovskite iridates having strong spin-orbit coupling. I will present the observation of such 3D Dirac semi-metallic ground state in AIrO3 (A = Ca, Sr) thin films using terahertz time-domain spectroscopy.

Mo-Po1-39
0.37 THz Gyro-TWA With A Cryo-free SCM: Design And Simulation
Craig Donaldson¹; Liang Zhang¹; Adrian Cross¹; Kevin Ronald¹; Alan Phelps¹; Wenlong He^2
1University of Strathclyde, United Kingdom; ²Shenzhen University, College of Electronic Science and Technology, China

This paper reports the work being carried out to realize a gyrotron-traveling wave amplifier operating at 372 GHz based on a helically corrugated interaction region (HCIR). The high magnetic field will be provided through a cryo-free superconducting magnet. There are many components in the waveguide circuit, which must achieve very low reflection targets. The design and simulation results of the gyro-TWA, the cusp electron beam source, the sub-millimetre wave components, as well as measurement of the HCIR will be presented in this paper.

Mo-Po1-40
Recent Results Of A CW, 94 GHz Second Harmonic Gyrotron Based On A Continuous Operation Solenoid
Dimin Sun; Tingting Zhuo; Guowu Ma; Linlin Hu; Hongbin Chen; Fanbao Meng
Institute of Applied Electronics, China Academy of Engineering Physics, China

Recent results of a CW, 94 GHz second harmonic gyrotron with a 1.8 T continuous operation solenoid are presented. The DC solenoid was cooled by water. Its inner bore diameter is 66 mm. The power consumption of the solenoid is 28 kW and the driving current is about 500 A. The gyrating electron beam was generated by a compact triode magnetic injection gun. A high efficiency internal quasi-optical mode converter with a pre-bunch quasi-optical launcher was used to separate the wave from the electron beam. The operating mode of the harmonic gyrotron is TE02. During the CW test, its operational frequency stabilized at 93.9 GHz. In the test, 5 min operation was realized. The output power is 12 kW with an electron beam of 45 kV, 1.6 A. The output efficiency is 24% with a single stage depressed collector.

Mo-Po1-41
Optimal Design Of A Magnetron Injection Gun For A 0.5 THz Continuously Frequency-tunable CW Gyrotron
Yanqing Zhang; Wei Wang; Tao Song; Jie Huang; Qiao Hu; Yichao Cao; Chen Zhang; Diwei Liu
UESTC, China

In this paper, the single anode magnetron injection gun with relatively low transverse velocity spread and high velocity pitch factor is designed for a 0.5THz continuously frequency-tunable CW gyrotron.

Mo-Po1-42
Electromagnetic Characteristics Of A Double Confocal Waveguide For A Gyro-TWT
Diwei Liu; Chen Zhang; Wei Wang; Tao Song; Qiao Hu; Yichao Cao; Yanqing Zhang
UESTC, China

There are two stable states existing in the double confocal waveguide, which are "superposition mode" and "ring mode". Compared the mode density in the double confocal waveguide with that in the single confocal waveguide and the cylindrical waveguide in the same frequency range, it is obvious that the mode density in the double confocal waveguides is relatively sparse. Hence, the double confocal waveguide has the characteristic of both mode selectivity and efficiency enhancement.

Mo-Po1-43
Study Of Low Voltage Angular Log-periodic Slow Wave Structure For 340 GHz TWT
Hexin Wang¹; Duo Xu¹; Xinyi Li²; Tenglong He¹; Zhanliang Wang¹; Ruichao Yang¹; Tao Tang¹; Zhaoyun Duan¹; Huarong Gong¹; Yanyu Wei¹; Yubin Gong^1
1University of Electronic Science and Technology of China, China; ²Nanjing Sanle Electronics Group Co., Ltd, China

A novel angular log-periodic groove waveguide slow wave structure (SWS) for 340 GHz traveling wave tube (TWT) is proposed in this paper. Due to the unique characteristics of log-periodic form, the novel SWS could achieve a very low operating voltage and small scale at the same time. By using the groove folded waveguide, the high aspect ratio fan-shaped sheet electron beam could interact with electromagnetic wave in the groove tunnel. According to direct mathematical equation, the operating voltage is 6310 V at 340 GHz and the total length of SWS is 8.6 mm, which could get an output power of 36 W with 20.7 dB gain.

Mo-Po1-44
A Novel Millimeter-wave Oversized Coaxial Relativistic Oscillator With Low Guiding Magnetic Field And High Power Capacity
Junpu Ling; Juntao He; Lili Song; Xingjun Ge; Jinchuan Ju; Bingfang Deng
College of interdisciplinary Studies, National University of Defense Technology, China

A novel Millimeter-wave oversized coaxial relativistic oscillator with low guiding magnetic field and high power capacity is proposed. The physical mechanism of this oscillator is investigated by theory and simulation. By introducing a coaxial structure and quasi body wave adopted as the operating mode, the oscillator can run stably under low guiding magnetic. Meanwhile, with an oversized structure and extended interaction extractor operating at higher order mode, the proposed oscillator has the potential of obtaining high output power close to Giggawatt-class. Main structure parameters are optimized by particle in cell simulations. Particle-in-cell simulations show that with the oversized coaxial structure, quasi body wave and extended interaction extractor operating at higher order mode, this proposed oscillator generates a 31 GHz, 840 MW microwave, while the diode voltage is 400 kV, the beam current is 6.1 kA, and the guiding magnetic field is 0.6 T. The corresponding power efficiency reaches 35%.

Mo-Po1-45
Terahertz-Infrared Spectroscopy Of Tm0.19Yb0.81B12 Dodecaboride
Elena Zhukova¹; Boris Gorshunov²; Andrey Azarevich³; Alexey Bogach³; Volodymyr B. Filipov⁴; Nataliya Yu. Shitsev⁴; Gennady A. Komandin³; Andrey V. Muratov⁵; Yuri A. Aleshchenko⁵; Nickolay E. Sluchanko^3
1Moscow Institute of Physics and Technology, Russian Federation; ²Moscow Institute of physics and technology, Russian Federation; ³Prokhorov General Physics Institute, Russian Academy of Sciences, Russian Federation; ⁴Frantsevich Institute for Problems of Materials Science, National Academy of Sciences of Ukraine, Ukraine; ⁵Lebedev Physical Institute, Russian Federation

First detailed measurements of terahertz-infrared electrodynamic response of high-quality single-crystalline Tm0.19Yb0.81B12 dodecaboride with dynamic charge stripes are performed at temperatures 5--300 K. Dramatic temperature changes in the dynamic conductivity spectra are observed, single-particle and collective excitations identified and their origin is discussed in terms of metal-insulator transition.

Mo-Po1-46
A Novel V-band Relativistic Transit-time Oscillator With High Power Handling Capacity
Bingfang Deng; Juntao He; Junpu Ling; Xingjun Ge; Jinchuan Ju
College of Advanced Interdisciplinary Studies, National University of Defense Technology, China

A novel V-band coaxial transit-time oscillator (TTO) with high power handling capacity is presented. The interaction region is designed to operate in TM02 mode to increase power handling capacity of the device. By using a traveling wave output structure, the saturation time of the device is improved, and the maximum surface electric field is decreased. The output structure is also good for improving beam-wave interaction. To avoid mode competition, deep corrugation is applied to the slow wave structure, so the Rayleigh hypothesis is not satisfied. Hence the dispersion relation of the SWS in output structure is analyzed by mode matching method instead of Floquet harmonic expansion method. In numerical simulation, a 642MW microwave pulse at 60.0GHz is obtained with a diode voltage of 400kV and beam current of 5kA. The power conversion efficiency is about 32.1%.

Mo-Po1-47
Development Of A 140 GHz 50kW Gyrotron In IAE
Linlin Hu; Guowu Ma; Dimin Sun; Tingting Zhuo; Qili Huang; Hongbin Chen; Fanbao Meng
Institute of Applied Electronics, China Academy of Engineering Physics, China

A 140GHz 50kWgyrotron as the first development stage in IAE-CAEP has been fabricated and tested. In the experiment, the gyrotron has achieved a reliable CW operation at 20kW for 60s, long-pulse operation at 30kW for 20s and repetitive pulse operation at 50kW for 30s with 60% duty cycle. The extension of pulse duration was hindered by the outgassing of BN window due to overheating. The results further confirmed that BN window has limited power capacity for high-frequency high-power gyrotrons. A gyrotron with a CVD diamond window has been fabricated. The experiment will be carried out in the next half of 2019.

Mo-Po1-48
Powerful Relativistic Oscillators Of THz-band Based On Excitation Of Talbot-type Supermode In An Oversized Cavity
Andrey Savilov; Yulia Oparina; Nikolai Peskov
Institute of Applied Physics RAS, Russian Federation

For relativistic oscillators, a new interaction regime is proposed based on the excitation of not a fixed transverse mode of the cavity, but a supermode formed by a fixed set of the transverse modes. Such regime is implemented in a quasi-optical cavity based on the Talbot effect, and allows to obtain narrow-band oscillation in a strongly oversized interaction space. Simulations of THz-band FEL with sub-GW to GW-level power driven by high-current relativistic electron beam are discussed

Mo-Po1-49
Investigation Of A Mini-Channel Cavity Cooling Concept For A 170 GHz, 2 MW Coaxial-Cavity Gyrotron
Stefan Illy; Konstantinos Avramidis; Philipp Bruecker; Gerd Gantenbein; Parth Kalaria; Sebastian Ruess; Manfred Thumm; John Jelonnek
Karlsruhe Institute of Technology / IHM, Germany

The maximum heat load on the cavity wall of high power fusion gyrotrons is one of the major limiting technological factors for the operation of the tube. To achieve the requested output power, efficiency and pulse length, a very efficient cooling of the interaction structure is mandatory. In this work, the performance of a mini-channel cavity cooling system for a 170 GHz, 2 MW coaxial-cavity gyrotron is numerically investigated, including the development of a mock-up test set-up for experimental validation.

Mo-Po1-50
Study On A Quasi-Optical Mode Converter For Gyrotron Based On Metamaterial
Wenjie Fu; Shijie Hu; Chaoyang Zhang; Xiaotong Guan; Yang Yan
University of Electronic Science and Technology of China, China

Artificial metamaterials offer unique functionalities for manipulating the spectral and spatial properties of electromagnetic waves in unconventional ways. In this paper, we report a transmission-type quasi-optical mode converter for gyrotron based on metamaterial. The initial simulation results show that the designed metamaterial quasi-optical mode converter is capable to transform the cylindrical TE01 mode to Gaussian beam, and the beam on the observed plane is with more than 95% scalar Gaussian mode content.

 

Mo-Po1-51
A Way To Match The Second Symmetric Mode Of Double-Grid Slow Wave Structure For Terahertz BWO
Yue Zhao¹; Hairong Yin¹; Jun Cheng¹; Yanyu Wei¹; Jin Xu¹; Lingna Yue¹; Jinjun Feng^2
1University of Electronic Science and Technology of China, China; ²Beijing Vacuum Electronics Research Institute, China

In this paper, a way to match the second symmetric mode of double-grid slow wave structure designed for a practical 1-THz terahertz backward wave oscillator is presented. Simulation results show that the return loss is less than -15 dB, and the insertion loss is about -4 dB in the 50-GHz operating bandwidth.

Mo-Po1-52
Project Of Relativistic Mm-wave Amplifier With Multi-pass Interaction
Alexander Leontyev; Edward Abubakirov; Andrey Konyushkov
Institute of Applied Physics of the Russian Academy of Sciences (IAP RAS), Russian Federation

The concept of the amplifier based on double amplification of symmetrical and non-symmetrical modes in relativistic traveling wave tube (TWT) with modulating resonator is described. The input signal excites E01 mode which goes through the first pass of amplification. The hybrid HE11 mode is used for the second pass of amplification and output. The simplified model of amplifier is built and theoretical research of the amplifier operation in the Ka band was performed. It was shown that the double pass interaction can provide more than 40 dB of gain along with 30-35% operation efficiency.

Mo-Po1-53
Characteristics Of A Low-Voltage Gyrotron Backward-Wave Oscillator
Chien-Lun Hung¹; Yi-Sheng Yeh²; Tsun-Hsu Chang^3
1National Penghu University of Science and Technology, Taiwan; ²Southern Taiwan University of Science and Technology, Taiwan; ³National Tsing Hua University, Taiwan

Gyrotrons are usually operated on high voltages to generate high power coherent radiation in the millimeter to terahertz band. Recently, some high frequency applications do not require high power sources. For such applications, lowing the voltage of a gyrotron becomes an important issue. This study analyzes linear and nonlinear characteristics of a gyrotron backward-wave oscillator (gyro-BWO) operating in low voltage regime. Simulation results predict that the start-oscillation current of a gyro-BWO increases rapidly when the voltage decreases to a lower limit. Moreover, the efficiency and the tuning bandwidth of a low-voltage gyro-BWO are investigated.

Mo-Po1-54
Propagation Characteristics Of Periodic Azimuthally Corrugated Waveguides Derived By The FDTD Code COCHLEA
Dimitrios Peponis; Georgios Latsas; Ioannis Chelis; Ioannis Tigelis
National and Kapodistrian University of Athens, Faculty of Physics, Greece

Azimuthal indentations have been proposed as an additional mean to suppress the parasitic oscillations in the gyrotron stacked beam-tunnel. As a first step, a smooth waveguide with azimuthal indentations was studied using COCHLEA code in order to identify their influence on the propagation characteristics. The S- parameters were calculated on the input and the output of the structure by decomposing the field into several modes. It was found that by increasing the indentations depth the field distributions change significantly and resonant effects are observed.

Mo-Po1-55
Design And Test Of 253/527 GHz Gyrotron for Spectroscopy Applications
Grigory Denisov¹; Mikhail Morozkin¹; Andrey Fokin¹; Alexey Chirkov¹; Andrey Kuftin¹; Sergei Kornishin¹; Evgeny Tai²; Anton Sedov¹; Mikhail Proyavin¹; Alexander Tsvetkov¹; Mikhail Glyavin^1
1Institute of Applied Physics of the Russian Academy of Sciences (IAP RAS), Russian Federation; ²GYCOM Ltd, Russian Federation

A 527 GHz continuous-wave second harmonic gyrotron is in development at the IAP RAS jointly with GYCOM Ltd. as a microwave source for spectrometry and diagnostics of various media. We present first results of experimental measurements of this gyrotron including output power, power losses in the cavity, wave beam profile, frequency, and spectrum.

Mo-Po1-56
Out-of-Equilibrium Electrons And Record Thermionic Emission In LaB6
Elena Zhukova¹; Boris Gorshunov¹; Martin Dressel²; Gennady A. Komandin³; Mickhail Bednyakov¹; Andrey V. Muratov⁴; Yuri A. Aleshchenko⁴; Mickhail Anisimov³; Nataliya Yu. Shitsevalova⁵; Anatoliy V. Dukhnenko⁵; Volodymyr B. Filipov⁵; Vladimir V. Voronov³; Nickolay E. Sluchanko^3
1Moscow Institute of Physics and Technology, Russian Federation; ²Physikalisches Institut, Universität Stuttgart, Germany; ³Prokhorov General Physics Institute, Russian Academy of Sciences, Russian Federation; ⁴Lebedev Physical Institute, Russian Federation; ⁵Frantsevich Institute for Problems of Materials Science, National Academy of Sciences of Ukraine, Ukraine

To understand mechanisms of high thermionic emission of LaB6 we use infrared spectroscopy, DC resistivity and Hall-effect techniques to study conduction electrons state in LaB6 single crystals with different contents of 10B and 11B isotopes. We find that up to 70% of conduction electrons are strongly non-equilibrium due to involvement in the collective oscillations of electron density coupled to vibrations of Jahn-Teller unstable boron cage and rattling modes of La-ions. We claim that these non-equilibrium electrons determine the extraordinary low work function of thermoemission in LaB6.

Mo-Po1-57
Efficiency Enhancement Of High-Harmonic Gyrotron By Stable Excitation Of High Axial Mode In The TWT Regime
Ilya Bandurkin; Yury Kalynov; Ivan Osharin; Andrey Savilov
Institute of Applied Physics of the Russian Academy of Sciences (IAP RAS), Russian Federation

The possibility of a stable excitation of a high axial mode in the traveling-wave tube regime in gyrotrons is demonstrated. Such an excitation becomes possible due to the use of a short element placed in the middle of the cavity and providing additional losses (either Ohmic losses or scattering into lower far-from-cutoff waves) for the near-to-cutoff first axial mode. This regime provides a significant efficiency enhancement in high-harmonic low-current gyrotrons.

Mo-Po1-58
Increasing The Diffraction Losses In Gyrotron Beam Tunnels For Improved Suppression Of Parasitic Oscillations
Ioannis Chelis¹; Dimitrios Peponis²; Georgios Latsas²; Ioannis Tigelis^2
1National and Kapodistrian University of Athens, Faculty of Physics, Greece; ²NKUA, Greece

High-power gyrotrons often suffer from parasitic oscillations in the compression region (beam tunnel) prior to the interaction cavity. A possible way to suppress the parasitic oscillations is to raise their starting currents by increasing the losses of the structure. In the present contribution we focus on the diffraction losses of the stacked copper-ceramic beam-tunnel concept. Parametric simulations show that the diffraction losses can be significantly increased by optimizing the geometric characteristics of the structure.

Mo-Po1-59
Wide Range Stepwise Frequency Tuning In Gyrotrons With Strong External Reflections
Irina Zotova¹; Naum Ginzburg¹; Andrey Malkin¹; Roman Rozental¹; Alexander Sergeev¹; Mikhail Glyavin¹; Seitaro Mitsudo²; Toshitaka Idehara^2
1Institute of Applied Physics RAS, Russian Federation; ²Research Center for Development of Far-Infrared Region, University of Fukui, Japan

We demonstrate that in a gyrotron with strong external reflections, frequency jumping in a wide range is possible due to sequential excitation of axial modes in the gyro-TWT regime. Within the frame of a time-domain model, the frequency tuning in the range of 202.3-206 GHz and the output power of 0.5 kW is shown, when modes with a number of axial variations from 1 to 10 are excited. The obtained parameters are suitable for the positronium spectroscopy in a Fabry-Perot resonator.

Mo-Po1-60
Design Of A Quasi-optical Mode Converter For A Dual-frequency Coaxial-cavity Gyrotron
Jianbo Jin; Gerd Gantenbein; Tobias Ruess; Manfred Thumm; John Jelonnek
Karlsruhe Institute of Technology / IHM, Germany

A quasi-optical mode converter is under development for an 170/204 GHz coaxial-cavity gyrotron at KIT, which is operated in the TE34,19 mode at 170 GHz and the TE40,23 mode at 204 GHz. A mirror-line launcher should be used for such modes with the ratio of caustic to launcher radius to be approximately 0.32. The optimum value of the launcher radius has been found to provide RF beams with relative high Gaussian-mode contents for both operation modes.

Mo-Po1-61
Linear Analyses Of A 0.22 THz Confocal Waveguide Gyro-TWT
Jie Yang¹; Shouxi Xu²; Yong Wang^2
1University of Chinese Academy of Sciences, China; ²Key Laboratory of High Power Microwave Sources and Technologies, Institute of Electronics, China

Confocal waveguide gyrotron traveling wave tube (gyro-TWT) is a novel gyrotron amplifier which can operate in higher order modes and generate high power. In this paper, the linear theory derived from kinetic theory is presented to analyze a 0.22-THz confocal waveguide Gyro-TWT which operates at HE06 mode. The linear gain is 9.6 dB/cm at 220.2 GHz. Different parameters are pointed out to show their influences on critical current of absolute instability.

Mo-Po1-62
Theoretical Research On 300GHz Carbon Nanotube Cold Cathode Gyrotron
Lulu Shao¹; Xuesong Yuan¹; Weifeng Li¹; Yu Zhang²; Bin Wang¹; Hailong Li¹; Yang Yan^1
1University of Electronic Science and Technology of China, China; ²Sun Yat-Se University, China

A 300 GHz carbon nanotube cold cathode TE03 gyrotron has been studied in this paper. Carbon nanotube cold cathode gun is optimized. Simulation results show that the average output power of 148 W has been obtained. This gyrotron experiment will be performed based on these parameters in the future.

Mo-Po1-63
Using Reflections For Suppressing Parasitic Oscillation In A Multimode Gyrotron
Maria Melnikova¹; Asel Adilova¹; Nikita Ryskin^2
1Saratov State University, Russian Federation; ²Saratov Branch, Institute of Radio Engineering and Electronics, RAS, Russian Federation

In recent years, the problem of control of gyrotron radiation by partial reflection of the output power from a remote load has attracted a considerable interest. In this paper, we study a reflection influence on mode-competition scenario in a multimode gyrotron. A possibility of controlling the mode competition processes by proper adjustment of reflection factors for different modes is discussed.

 

Mo-Po1-64
Simulations Of Sub-THz Confocal-Cavity Gyrotrons With Different Configurations Of Electron Beams
Mikhail Glyavin; Vladislav Zaslavski; Vladimir Manuilov; Irina Zotova; Dmitry Sobolev
Institute of Applied Physics Russian Academy of Sciences (IAP RAS), Russian Federation

Based on 3D PIC (particle-in-cell) simulations, we conduct a comparative analysis of operation of sub-THz confocal-cavity gyrotrons with two configurations of a driven electron beam namely, a conventional cylindrical hollow electron beam and a sheet rotating electron beam injected midway between the cavity mirrors. It is demonstrated, that for parameters of the experimentally realized 140 GHz confocal gyrotron, the starting and operating current can be significantly decreased with using the sheet rotating electron beam, while the efficiency of generation increases at least in 1.5 times (up to 30-35%). The smooth frequency tuning of 5% by mechanical variation of the distance between mirrors are also demonstrated.

Mo-Po1-65
Development Of 100 MW W-Band Gyrotron With Relativistic Sheet Electron Beam
Naum Ginzburg¹; Andrey Malkin¹; Roman Rozental¹; Vladislav Zaslavsky¹; Ilya Zheleznov¹; Vladimir Tarakanov^2
1Institute of Applied Physics of the Russian Academy of Sciences (IAP RAS), Russian Federation; ²Moscow Engineering Physics Institute, Russian Federation

Based on 3D PIC-simulations we study a possibility of development of a high-power W-band gyrotron driven by a sheet large-aperture relativistic electron beam. Improvement in selectivity can be provided by using a planar cavity, which is partially open over transverse (with respect to a beam motion) direction. It was demonstrated that for 500 keV/1 kA electron beam with the transverse size of ten wavelengths, a single-mode generation with 100 MW output power and efficiency of 20% can be obtained in the considered scheme.

Mo-Po1-66
Development Of Powerful W-band Planar Surface-Wave Oscillator Driven By High-Current Relativistic Sheet Electron Beam
Nikolai Peskov¹; Andrey Arzhannikov²; Naum Ginzburg¹; Petr Kalinin²; Tatiana Krapivnitskaya¹; Eugene Sandalov²; Alexander Sergeev¹; Stanislav Sinitsky²; Vasily Stepanov²; Vladislav Zaslavsky^1
1Institute of Applied Physics RAS, Russian Federation; ²Budker Institute of Nuclear Physics RAS, Russian Federation

Project of powerful planar W-band surface-wave oscillator is under development in collaboration between IAP RAS (N.Novgorod) and BINP RAS (Novosibirsk) at the "ELMI" accelerator 1 MeV / 5 - 7 kA / 3 ÃfÆ'ââ,¬Å¡Ãfâ?sÃ,µs. Electrodynamic system of this oscillator is based on a two-dimensional doubly-periodical structure, which combines properties of a slow-wave system that realizes conditions for an effective Cherenkov interaction with a high-current rectilinear sheet electron beam, and a high-Q resonator that implements mechanism of two-dimensional distributed feedback and provides selective excitation of the operating mode in the strongly oversized interaction space. Design parameters of the project are discussed and results of the simulations are presented, which demonstrate possibility to achieve in the considered scheme a stable narrow-band regime of oscillation with output power of the gigawatt level.

Mo-Po1-67
Spectral Radiation Pattern Of Bulk Waves Emitted By Thermally Stimulated Surface Plasmons At The Sample Edge
Ildus Khasanov¹; Alexey Nikitin²; Vasily Gerasimov^3
1Scientific and Technological Center of Unique Instrumentation of the Russian Academy of Sciences, Russian Federation; ²Scientific and Technological Center for Unique Instrumentation of RAS, Russian Federation; ³Budker Institute of Nuclear Physics SB RAS, Russian Federation

It was shown that the edge of a metal body face emits narrowly directed IR radiation with a spectrum of blackbody type, due to the surface plasmon nature of this radiation. Here we present the results of studies showing that the direction of the radiation pattern depends on its spectral composition. This confirms applicability of the analytical model for the diffraction field of monochromatic surface plasmon-polaritons (SPPs) to the case of broadband TSPPs.

Mo-Po1-68
High-Efficiency Gyrotron With Beam Energy Recovery
Oleg Louksha; Pavel Trofimov
Peter the Great St. Petersburg Polytechnic University, Russian Federation

This paper presents results of the combined 3-D simulation of a 74.2 GHz, 100 kW gyrotron with a four-stage depressed collector. The maximum overall efficiency of 72 % has been achieved as a result of improvement of electron beam quality and effective recovery of spent beam energy.

Mo-Po1-69
Compact Pulsed Magnets Designed For An 800 GHz, 2th Harmonics Gyrotron
Pengbo Wang¹; Houxiu Xiao¹; Donghui Xia²; Xin Qi¹; Liang Li¹; Xiaofeng Li¹; Xianfei Chen^1
1Huazhong University of Science and Technology, Wuhan National High Magnetic Field Center, China; ²Huazhong University of Science and Technology, School of Electrical and Electronics Engineering, China

This paper proposes the design of compact pulsed magnets for high frequency gyrotrons. With 12 layers of helices reinforced by zylon fibers, the pulsed magnet provides a magnetic field of 14.8 T for the 800 GHz gyrotron operating at the second harmonics. The pulse duration can be as much as 165 ms, and a pitch factor of 1.32 and a transverse velocity spread of 5.12% were obtained with the given electron gun geometry.

Mo-Po1-70
Design Of Quasi-Optical Mode Converter For 28GHz Gyrotron
Qili Huang; Dimin Sun; Linlin Hu; Tingting Zhuo; Guowu Ma; Hongbin Chen
Institute of Applied Electronics, China Academy of Engineering Physics, China

This paper presents the design of two quasi-optical mode converter for gyrotrons to transform the cavity waveguide mode TE02 and TE83 into a fundamental Gaussian beam. Those two quasi-optical mode converters are optimized by a combination of three methods, which are the scalar diffraction theorem, the K-S phase-correcting optimization iterative algorithm, and Geometrical Optics. According to the results, the conversion efficiency of energy is 92.5%( TE02) and 95%( TE83) and the Gaussian content of the output beam on the window surface is 99%.

Mo-Po1-71
Performance Tests Of ITER Gyrotrons And Design Study Of Dual-frequency ITER Gyrotron
Ryosuke Ikeda; Ken Kajiwara; Taku Nakai; Takayuki Kobayashi; Masayuki Terakado; Koji Takahashi; Keishi Sakamoto
National Institutes for Quantum and Radiological Science and Technology, Japan

Performance tests for two ITER gyrotrons have being carried out in the QST. In the tests, the output power of 1.05 MW with efficiency of 50.5 % for 300 s, the output power of 0.9 MW for 60 s in the 5 kHz full-modulation, and operation reliability of more than 90 % were achieved. Design study of dual-frequency gyrotron has been carried out to apply plasma operations at 1.8 T, 2.65 T and 5.3 T in ITER. It succeeded in design values of power transmission efficiencies in 104 GHz and 170 GHz oscillations almost equivalent to the design value in the current ITER gyrotron.

Mo-Po1-72
Double-Anode Sheet-Beam Electron Gun With A Circular Cathode For 220 GHz TWT
Shengkun Jiang¹; Zhaoyun Duan¹; Guang Yang¹; Tao Tang¹; Zhanliang Wang¹; Huarong Gong¹; Yubin Gong¹; Ye Tang²; Pan Pan²; Jun Cai²; Jinjun Feng^2
1School of Electronic Science and Engineering, University of Electronic Science and Technology of China, China; ²National Key Laboratory of Science and Technology on Vacuum Electronics in Beijing, Beijing Vacuum E, China

A 220 GHz double-anode sheet-beam electron gun with a circular cathode is designed using the three-dimensional particle simulation software Opera 18R2. The simulated results of beam current and the size of the beam waist are 140 mA and 0.5 mmÃfÆ'ââ,¬"0.1 mm at z=9 mm, respectively. This proposed double anode sheet beam electron gun is used in a T-shape staggered double-grating traveling wave tube (TWT).

Mo-Po1-73
TM-Mode Gyrotrons
Tsun-Hsu Chang
Department of Physics, National Tsing Hua University, Taiwan

Transverse magnetic (TM) waveguide modes have long been considered as the unsuitable modes for the operation of the electron cyclotron maser (ECM). This study reveals that certain TM modes might be suitable for gyrotrons --- ECM based devices. Unlike transverse electric (TE) modes, the linear behavior of the TM modes depends on the sign of the wave number kz. The negative kz has much stronger linear efficiency than that of the positive kz. In addition, the non-linear calculation for a fixed field profile shows that the efficiency of some TM modes could be as high as that of the TE modes. The current findings are encouraging and imply that TM modes might be advantageous to the gyrotron backward-wave oscillators.

Mo-Po1-74
Research On Y-Band Double Grating Diffraction Radiation Oscillators
Yaming Chen; Yaxin Zhang; Yilin Pan; Hexin Wang; Kaicheng Wang; Zhanliang Wang; Yubin Gong
University of Electronic Science and Technology of China, China

An open resonance systems (ORS) composed of cylindrical mirror and planar mirror was combined with double comb gratings, which was investigated in this paper. The results show that in such structure the electron beam will interacts with the quasi-optical mode in the cavity efficiently. The output power can reach to more than 3 W at 0.33 THz with about 2 GHz band width. This radiation system provides a potential way to develop high power and compact THz sources.

Mo-Po1-75
Study On The Beam-wave Interaction In A 28GHz Gyrotron With Complex Cavity
Yanwei Lu; Sheng Yu; Zhipeng Wang; Tianzhong Zhang; Rutai Chen; Wenjing Huang; Jin Luo
University of Electronic Science and Technology, China

In this paper, a 28GHz gyrotron with gradually tapered complex cavity is simulated and designed. In order to achieve high efficiency, we analyse the influences of the structural parameters on interaction efficiency, the effects of the electron beam parameters are also analyzed. The simulation results shows that the designed gyrotron can obtain output power of 43.18kW when the beam current is 2.1A, beam voltage is 53kV. The corresponding efficiency can reach to 38.80%.

Mo-Po1-76
Study On Hollow Cavity Of 140-GHz Gyrotrons
Yichi Zhang¹; Bentian Liu^2
1Beijing Vacuum Electronics Research Institute, China; ²National Key Laboratory of science and technology on Vacuum Electronics, China

To design an hollow cavity of 140-GHz Gyrotron, we conducted a study for TE22,6 mode cavity. Through changing magnetic field strength, voltage, current, radius and length of cavity, we analyzed the influence factors of structural parameters and electrical parameters on working performance. Under the experimental conditions of voltage 70kV and current 35A, we got a result which approximately the same with output power in fact.

Mo-Po1-77
Analysis On Resonator Coupling Characteristics Of Sub-THz EIA
Qinqin Yuan; Ziqiang Yang; Zongjun Shi; Ting Zhang; Xiaopin Tang; Feng Lan
Terahertz Science Cooperative Innovation Center, University of Electronic Science and Technology, China

The resonator coupling characteristics of Sub-THz extended interaction amplifier (EIA) with the grating and sub-wavelength hole array structure is simulated at the TM31-2π mode. Zero-field points of TM31-2π modes at the center of the beam tunnel promote an effective beam-wave interaction. The operating frequency of the intermediate cavity is 231.28 GHz with characteristic impedance of 207.74 Ω. The return losses of the input and output cavity are both better than 11.32 dB at 231.1 GHz, and the -3 dB bandwidth is 984 MHz.

Mo-Po1-78
Multiphonon Anharmonicity In MgO An Ionic Binary Compound
Paola Giura¹; Lorenzo Paulatto²; Daniele Antonangeli²; Fei He²; Ricardo P. S. M. Lobo³; Eugenio Calandrini²; Alexei Bosak⁴; Luigi Paolasini^4
1Sorbonne-University, France; ²IMPMC Sorbonne university, UMR CNRS 7590, France; ³ESPCI, LPEM, France; ⁴ESRF, France

The anharmonic lattice dynamics of MgO has been studied at ambient conditions and at high temperatures by infrared spectroscopy combined with density functional perturbation theory calculations. The agreement between the measured phonon energies and widths with ab-initio calculated values provides a direct and pertinent test of the validity of advanced theoretical methods. Long observed anharmonic features in the infrared reflectivity find a clear explanation in terms of well-defined multi-phonons scattering processes and lattice dynamics peculiarities, also responsible of a significant and sharp reduction of the longitudinal optical phonon lifetime at critical finite wave vectors. Our work highlights the importance of multi-phonons scattering processes on collective dynamics and related material properties

Mo-Po1-79
Pulsed Gyrotron Start-up Scenario In Presence Of Voltage/Current Surge Front
Yulia Novozhilova¹; Nikita Ryskin²; Mikhail Glyavin¹; et al^1
1Institute of Applied Physics RAS, Russian Federation; ²Branch, Kotel'nikov Institute of Radio Engineering and Electronics RAS, Russian Federation

The possibility of high-efficiency single-mode regimes in a sub-megawatt power 250-GHz gyrotron, which is developed for the DEMO project, is studied. Nonlinear mode interaction at the front of accelerating voltage pulse/current is discussed. It is shown that for these scenarios a single-mode high-efficiency regime is possible within a fairly broad band of cyclotron frequency mismatch. Stability of such a regime with respect to the excitation of spurious modes is studied.

Mo-Po1-80
Powerful 1 THz Third-Harmonic Gyrotron For Plasma Applications
Yuriy Kalynov; Ilia Bandurkin; Vladimir Manuilov; Ivan Osharin; Andrey Savilov; Nikolai Zavolsky
Institute of Applied Physics of the Russian Academy of Sciences (IAP RAS), Russian Federation

The possibility of creating a third-cyclotron-harmonic large-orbit gyrotron with a radiation frequency of 1 THz and an output power of several kilowatts for its use in promising plasma studies is studyed.

 

Mo-Po1-81
Competition Of Oscillations At Different High Cyclotron Harmonics In The Sub-THz Large-Orbit Gyrotron
Yuriy Kalynov; Ivan Osharin; Andrey Savilov
Institute of Applied Physics of the Russian Academy of Sciences (IAP RAS), Russian Federation

Recently, 30 keV/0.7A CW sub-THz large-orbit gyrotron have been experimentally realized. Two different modes at different (second and third) cyclotron harmonic were excited in the same cavity separately at slightly different magnetic fields. This work is dedicated to description of various regimes of competition of the two modes observed in the experiment.

Mo-Po1-82
1.0 THz BWO Based On Novel Helical Groove Rectangular Waveguide
Zhigang Lu; Ruidong Wen; Zhicheng Su; Weihua Ge; Tao Tang; Huarong Gong; Yubin Gong
University of Electronic Science and Technology of China, China

A novel helical groove rectangular waveguide slow wave structure (HGRW-SWS) is put forward to develop the lower operating voltage and high electron efficiency terahertz backward wave oscillator (BWO). The major advantage of the HGRW structure is its higher interaction impedance, lower ohm loss and lower operating voltage with respect to the typical SWSs such as folded waveguide SWS or double staggered grating SWS especially in the case of higher spatial harmonics. It is found that this kind of SWS can be operating on the n=-2 harmonic with the interaction impedance of more than 1.5 ohms from the analysis of the cold characteristics of the HGRW-SWS. Moreover, the beam-wave interaction results indicate that the BWO based on the HGRW SWS can produce the output power exceeding 0.657 W in the frequency range from 0.894 THz to 1.164 THz.

Mo-Po1-83
Two-dimensional Particle Simulation Analysis Of Ion Noise In TWT
Zhixin Yang; Zugen Guo; Rujing Ji; Zhigang Lu; Zhaoyun Duan; Yubin Gong; Huarong Gong
National Key Laboratory of Science and Technology on Vacuum Electronics, University of Electronic Science and Technology, China

In this paper, we establish a calculable TWT model to analyze the ion noise and adopt the intensity of fluctuation frequency and amplitude of ions and the average kinetic energy of electrons to indicate the strength of ion noise. The relationship between ion noise and the magnetic field is discussed. An effective way to suppress ion noise is adjustment of the magnetic field so that the interaction length is an integral multiple of the scalloping wavelength, decrease the accumulation of ions. The simulation results are consistent with the theoretical analysis.

Mo-Po1-84
Design Of Electron Optical System For 0.22THz Folded Waveguide TWT
Zugen Guo; Zhixin Yang; Rujing Ji; Ping Han; Lu Zhigang; Yubin Gong; Huarong Gong; Zhanliang Wang; Tao Tang
University of Electronic Science and Technology of China, School of Electronic Science and Engineering , China

An electron optical system(EOS) of 0.22THz folded waveguide travelling-wave tube (FW-TWT) was designed in this paper. The design process of Pierce gun and periodic permanent magnet focusing system was introduced in detail. The electromagnetic field simulation software Opera-3D was used to simulate and optimize the magnetic field. This simulation results show that the electron optical system transmitted beam current 33mA, cathode voltage -19kV, the first anode -3kV, and the beam transmission rate was 100%.

 

Mo-Po1-85
Analysis Of Folded Waveguide TWT With Non-Central Double Beams
Duo Xu¹; Wei Shao¹; Tenglong He¹; Hexin Wang¹; Zhanliang Wang¹; Zhigang Lu¹; Huarong Gong¹; Zhaoyun Duan¹; Jinjun Feng²; Yubin Gong^1
1University of Electronic Science and Technology of China, China; ²Beijing Vacuum Electronics Research Insitute, China

In order to increase the output power of the folded waveguide (FW) Traveling wave tube (TWT), a novel Non-Central double beams (NCDB) FW-TWT is proposed in this paper. Compared with the traditional central beam (CB) FW-TWT, the NCDB-FW-TWT can double the output power without increasing the current of the single beam. A W-band NCDB-FW-TWT is designed in this paper. The PIC simulation results show that the maximal output power can reach 90 W and the 3-dB over 8.8%.

Mo-Po1-86
Cusp Electron Gun With Modulation Electrode For A THz Gyro-amplifier
Liang Zhang¹; Craig Donaldson²; Wenlong He³; Alan Phelps⁴; Adrian Cross^1
1University of Strathclyde, United Kingdom; ²Department of Physics, University of Strathclyde, United Kingdom; ³Shenzhen University, College of Electronic Science and Technology, China; ⁴University of Strathclyde, Department of Physics, United Kingdom

A terahertz gyrotron traveling wave amplifier (gyro-TWA) centered at 370GHz is under development for the electron paramagnetic resonance (EPR) imaging application. This paper reports the investigation of a triode-type cusp electron gun for the terahertz gyro-TWA. The simulation results showed that at the beam alpha (the ratio of transverse to axial velocity) center of 1.07, an optimal alpha spread of ~10% was achieved, when it was operated at a beam voltage of 50 kV and a beam current of 0.35 A.

Mo-Po1-87
Possibilty of Super-Radiance At The Frequencies Of 3-5 THz From Short Electron Bunches Moving In Micro-Ondulators
Nezah Balal; Vladimir L. Bratman; Yuri Lurie
Ariel University, Israel

An available frequency range of coherent radiation from ps bunches with high charge can be significantly enhanced if one uses a micro-undulator with a high transverse field. Such an undulator with a helical symmetry can be implemented by redistributing a strong uniform magnetic field by a helical ferromagnetic insertion. Simulations demonstrate that using such undulators with period of 8-10 mm enable efficient coherent spontaneous radiation from short bunches with durations of (0.08-0.15) ps and super-radiance from extended bunches with duration of about 2 ps in frequency range of 3-5 THz.

Mo-Po1-88
Experimental Results Of Spectral And Imaging From Tunable Coherent Terahertz Radiation
Xuling Lin¹; Jianbing Zhang²; Zhimin Dai²; Zhi Zhang^1
1Beijing Institute of Space Mechanics and Electricity, China; ²Shanghai Institute of Applied Physics, Chinese Academy of Sciences, China

In this paper, we demonstrate the generation and observation of watt-level, coherent tunable terahertz radiation from relativistic femtosecond electron beam. Spectral content of the coherent terahertz emission from the undulator and dipole magnet is measured, and high quality terahertz imaging experimental is carried utilizing methodology of super-resolution reconstruction.

 

Mo-Po1-89
Studying Mechanical Properties And Phase Transitions Of Aspirin Polymorphs With Terahertz Spectroscopy And Ab Initio Simulations
Qi Li¹; Andrew Bond²; Axel Zeitler^1
1University of Cambridge, United Kingdom; ²University of Cambridge, Department of Chemistry, United Kingdom

Subtle structural differences and comparable lattice energies have triggered controversial discussions on the stabilities, mechanical properties and further comparisons between two polymorphs of aspirin. In this study, terahertz time-domain spectroscopy (THz-TDS) is coupled with density functional theory (DFT) and ab initio molecule dynamics (AIMD) calculations to seek physical insight into the properties of crystalline aspirin. Large-size supercells incorporating defects are used to simulate disorder in the aspirin crystal structure to investigate possible mechanisms for polymorphic transformation. THz-TDS of aspirin single crystals is performed to investigate certain interesting modes that may play a critical role in the phase transitions and mechanical properties of aspirin.

Mo-Po1-90
Anisotropic MagnetoResistance Of 3d Ferromagnetic Metals Observed by THz-TDS
JiHo Park¹; Soo gil Lee¹; Jeong Mok Kim²; Nyun Jong Lee³; Sanghoon Kim³; Byong Guk Park²; Kab Jin Kim^1
1Department of Physics, KAIST, Republic of Korea; ²Department of Materials Science and Engineering, KAIST, Republic of Korea; ³Department of Physics, University Of Ulsan, Republic of Korea

Electrical resistance of magnetic materials depends on magnetization orientation of the sample. The representative example is anisotropic magnetoresistance (AMR)[1]. Despite a number of experimental reports, our understanding on the microscopic origin of AMR is still far from complete. Theory has predicted that the AMR originates from different electronic scattering from conduction s,p and d bands to localized d band [2] which is closely related to spin orbit coupling (SOC). However, the microscopic mechanism underlying the scattering process is yet to be fully understood experimentally. Therefore, a direct measurement of electron scattering is important for revealing the origin of AMR. Using THz-TDS, here we directly access the scattering time of conduction electron in 3d metallic ferromagnets.

Mo-Po1-91
Tilted-Pulse-Front Pumped Plane-Parallel LiNbO3 Slab THz Source
Priyo Nugraha; Gergo Krizsan; Csaba Lombosi; Laszlo Palfalvi; Gyorgy Toth; Gabor Almasi; Janos Hebling; Jozsef Fulop
Institute of Physics, University of Pecs, Hungary

A new type of tilted-pulse-front pumped terahertz (THz) source has been demonstrated, which is based on a LiNbO3 plane-parallel slab with an echelon structure on its input surface. The use of a plane-parallel nonlinear optical crystal slab enables straightforward scaling to high THz pulse energies and the production of a symmetric THz beam with a uniform pulse shape for good focusability and high field strength.

Mo-Po1-92
Terahertz Plasmonic Photocurrents In Graphene Nanostructures
Viacheslav Popov; Denis Fateev
Kotelnikov Institute of Radio Engineering and Electronics, Russian Federation

The theory of plasmon detection of terahertz radiation in a periodic graphene structure with spatially inhomogeneous graphene near the Dirac point is developed.

 

Mo-Po1-93
Development Of The Second Harmonic 190 GHz Gyrotron For OAM Communication
Ashwini Sawant; Ingeun Lee; Mun Seok Choe; EunMi Choi
Ulsan National Institute of Science and Technology (UNIST), Republic of Korea

We presented the design of a 190 GHz second harmonic gyrotron capable of generating few kWs of power in a mode-pair TE8,3 and TE11,2 at 33 and 37 kV voltage respectively. Conventional cavity with two sinusoidal perturbations has been used to reduce the mode competition from fundamental mode. It is designed for the conceptual study of OAM communication using gyrotron mode.

Mo-Po1-94
Design And Fabrication Of A D-Band Traveling Wave Tube For Millimeter Wave Communications
Rupa Basu; Laxma Billa; Jeevan Rao; Rosa Letizia; Claudio Paoloni
Lancaster University, United Kingdom

The design and fabrication aspects of a novel D-band (141 GHz-148.5 GHz) Traveling Wave Tube (TWT) for enabling the first point to multipoint front end at D-band, objective of European Commission H2020 ULTRAWAVE is presented. The ULTRAWAVE system will provide unprecedented wireless area capacity over wide area sectors, with radius up to 500 - 600 m for the future 5G high density small cell deployment. The design and fabrication processes adopted for the TWT are focused to find new low cost solutions for TWTs at millimetre waves to satisfy the requirements of the wireless market. The proposed TWT will provide more than 10 W saturated output power for achieving more than 100 Gb/s/km2 of area capacity over 600 meters radius wide angle sector, with 99.99% availability in ITU zone K.

Mo-Po1-95
Development Of High-Harmonic CW Gyrotron With An Operating Frequency Of 1.2 THz
Alexander Tsvetkov¹; Vladimir Manuilov¹; Irina Zotova¹; Ilya Bandurkin¹; Alexey Fedotov¹; Vladislav Zaslavsky¹; Yoshinori Tatematsu²; Seitaro Mitsudo²; Toshitaka Idehara²; Mikhail Glyavin^1
1Institute of Applied Physics RAS, Russian Federation; ²Research Center for Development of Far-Infrared Region, University of Fukui, Japan

The report is devoted to development of a 3d harmonic CW gyrotron with the record output frequency of 1.2 THz. Based on analyses of start currents we demonstrate, that improvement of mode selectivity can be achieved due to interaction with an electron beam having a specially increased (up to 30-40%) velocity spread. In such conditions the start current of a near-cutoff operating mode decreases due to influence of "slow" electron fractions in the electron beams. At the same time, the start currents of parasitic modes, which are very sensitive to the velocity spread, increases significantly. The suppression of spurious mode and selective excitation an operating TE15,6 mode is demonstrated in the frame of 3D particle-in-cell simulations using CST STUDIO SUITE.

Mo-Po1-96
The Effect Of The Lossy Material On The Modes In A Smooth Metallic Dielectric Loaded Gyrotron Beam Tunnel
George Latsas¹; Ioannis Tigelis¹; Jeremy Genoud²; Stefano Alberti^2
1National and Kapodistrian University of Athens/ Faculty of Physics, Greece; ²École Polytechnique Fédérale de Lausanne, Swiss Plasma Center, Switzerland

The effect of the dielectric material on the dispersion properties and behavior of the modes in a smooth metallic gyrotron beam tunnel, partially filled with a lossy dielectric material, is studied. Two kinds of modes were identified, one located inside the empty region and the other inside the dielectric region. It was seen that these two kinds of modes are not equally affected by the changes in the geometry and dielectric characteristics.

Mo-Po1-97
Design Of An 800GHz Gyrotron
Xianfei Chen; Houxiu Xiao; Tao Peng; Donghui Xia; Xin Qi; Pengbo Wang
Wuhan National High Magnetic Field Center, Huazhong University of Science and Technology, China

The design of an 800GHz gyrotron with output power of 172kW is presented. This gyrotron operates at fundamental resonance with a 30T pulsed magnet. The parameters are optimized according to the normalized parameters. The simulation results show that the maximum efficiency of 43% can be reached.

Mo-Po1-98
Experimental Study Of The Emission Properties Of Magnetron Injection Guns For High-Power Gyrotrons
Zisis Ioannidis; Tomasz Rzesnicki; Ioannis Pagonakis; Gerd Gantenbein; John Jelonnek
Karlsruhe Institute of Technology, Germany

The quality of the electron beam generated by a magnetron injection gun (MIG) is very important in order to ensure the excellent performance of high-frequency, high-power gyrotrons. A diagnostic device, operating at scaled down parameters, was recently developed at KIT in order to study the emission properties of various MIGs that are used with prototype modular short-pulse gyrotrons. Herein, we present the first experimental results that were obtained for electron guns that are used with coaxial 2 MW, 170 GHz gyrotrons.

Mo-Po1-99
Electrically-controlled THz Emission From AlGaN/GaN/Al2O3 High Electron Mobility Transistor Structures At A Temperature Of 20 K
Ignas Grigelionis¹; Pawel Prystawko²; Irmantas Kasalynas^1
1Center for Physical Sciences and Technology, Lithuania; ²Institute of High Pressure Physics UNIPRESS, Poland

We investigated radiative phenomena contributing to the THz emission of AlGaN/GaN high electron mobility transistor (HEMT) structures grown on sapphire substrate. Electrically controlled emission spectroscopy was performed in the frequency range 100-600 cm-1 at a temperature of 20 K. The electroluminescence from nitrogen vacancies in GaN buffer layer contributed to the THz emission spectrum, and the amplitude and frequency of the observed narrow emission lines were controlled by applied voltage.

Mo-Po1-100
Electric Dipole-free Meta-cylinders
Mahdi Safari¹; Ali Momeni²; Ali Abdolali²; Nazir P. Kherani^1
1Department of Electrical and Computer Engineering, University of Toronto, Canada; ²Department of Electrical Engineering, Iran University of Science and Technology, Iran

In this paper, we propose a novel asymmetrical meta-atom for control of electromagnetic wave based on analytical formulation. Here, we show that the proposed meta-cylinder is flexible and well capable of achieving exotic electromagnetic responses.