Special Issue for the 4th Shenzhen International Conference on Advanced Science and Technology（SICAST 2013）Part I
The 4th SICAST held in Shenzhen during 3-9 November 2013 has achieved overwhelming success. There are 28 talks with high international standard and quality, including 18 talks by famous scientists from 8 countries and 10 talks by Chinese young scientists. The subjects of the presentations covered a wide scale from pure and fundamental THz science to THz applications, all presentations were followed by extensive discussions at the conference. Due to the finite attendees who can be invited to the GORDON-type SICAST conference, we wish TST’s successive publication of the special issues on the talks of SICAST can give enlightening to the researchers in THz field. Editorial office would also extend appreciation to all authors for their collaboration and support to this special issue.
The New Year 2014 is coming soon. Editorial office would like to give all of you our sincere greeting: Happy New Year!
TST, Vol. 6, No. 4, PP. 212-222
(Invited paper) Multi-frequency notch filters and corrugated 200 to 400 GHz waveguide components manufactured by stacked ring technology
M. Thumm 1*, D. Wagner 2, E. de Rijk 3, W. Bongers 4, W. Kasparek 5, F. Leuterer 2, A. Macor 3, J.-Ph. Ansermet 6, F. Monaco 2, M. Münich 2, H. Schütz 2, J. Stober 2, H. v.d. Brand 4, and A.v. Bieren 3
1 Karlsruhe Institute of Technology (KIT), IHM and IHE, Karlsruhe, Germany
2 Max-Planck-Institut für Plasmaphysik (IPP), EURATOM-IPP, Garching, Germany
3 SWISSto12 SA, Science Park - EPFL, Lausanne, Switzerland
4 Dutch Institute for Fundamental Energy Research, EURATOM-DIFFER, Nieuwegein , Netherlands
5 Institut für Grenzflächenverfahrenstechnik und Plasmatechnologie (IGVP) , Universität Stuttgart, Germany
6 Laboratoire de Physique des Matériaux Nanostructurés, EPFL, Lausanne, Switzerland
*1 Email: email@example.com
(Received November 30, 2013)
Abstract: Sensitive millimeter wave diagnostics need often to be protected against unwanted radiation like, for example, stray radiation from high power Electron Cyclotron Heating applied in nuclear fusion plasmas. A notch filter based on a waveguide Bragg reflector (photonic band-gap) may provide several stop bands of defined width within up to two standard waveguide frequency bands. A Bragg reflector that reflects an incident fundamental TE11 into a TM1n mode close to cutoff is combined with two waveguide tapers to fundamental waveguide diameter. Here the fundamental TE11 mode is the only propagating mode at both ends of the reflector. The incident TE11 mode couples through the taper and is converted to the high order TM1n mode by the Bragg structure at the specific Bragg resonances. The TM1n mode is trapped in the oversized waveguide section by the tapers. Once reflected at the input taper it will be converted back into the TE11 mode which then can pass through the taper. Therefore at higher order Bragg resonances, the filter acts as a reflector for the incoming TE11 mode. Outside of the Bragg resonances the TE11 mode can propagate through the oversized waveguide structure with only very small Ohmic attenuation compared to propagating in a fundamental waveguide. Coupling to other modes is negligible in the non-resonant case due to the small corrugation amplitude (typically 0.05·l0, where l0 is the free space wavelength). The Bragg reflector was optimized by mode matching (scattering matrix) simulations and manufactured by SWISSto12 SA, where the required mechanical accuracy of ± 5 mm could be achieved by stacking stainless steel rings, manufactured by micro-machining, in a high precision guiding pipe (patent is pending). The two smooth-wall tapers were fabricated by electroforming. Several measurements were performed using vector network analyzers from Agilent (E8362B), ABmm (MVNA 8-350) and Rohde&Schwarz (ZVA24) together with frequency multipliers. The stop bands around 105 GHz (-55dB) and 140 GHz (-60dB) correspond to the TE11-TM12 and TE11-TM13 Bragg resonances. Experiments are in good agreement with theory. The stacked rings technology has also been employed for manufacturing of oversized (I.D. = 15 mm) corrugated waveguides (propagating the balanced HE11 hybrid mode). The waveguides are for use in a 4 m long transmission line for Dynamic Nuclear Polarization Nuclear Magnetic Resonance applications in the 200 to 400 GHz band. A high performance flange connection system between the modules allows for modular path building. To validate the performance of the proposed system, a detailed characterization of all corrugated waveguide components has been performed using a Vector Network Analyzer operating in the 220 to 330 GHz range.
Keywords: Electron cyclotron heating, Gyrotrons, Plasma diagnostics, Bragg reflector notch filter, Dynamic nuclear polarization, Oversized Terahertz HE11-mode transmission line, Stacked rings manufacturing technology
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TST, Vol. 6, No. 4, PP. 223-233
(Invited paper) The linear and non-linear THz properties of graphene
Kai Yang, Sara Arezoomandan, and Berardi Sensale-Rodriguez *
The University of Utah, Department of Electrical and Computer Engineering,
50 S. Central Campus Dr., Salt Lake City, UT 84112, USA
* Email: firstname.lastname@example.org
(Received December 9, 2013)
Abstract: Graphene has recently been the subject of much attraction for THz applications due to its extraordinary material properties arising from its particular band structure. This paper reviews and discusses the linear and nonlinear properties of graphene at microwave/THz frequencies, and it also compares these properties with those of other semiconducting materials. By taking into account the effect of electron momentum relaxation time on intra-band optical transitions, which is significant at microwave and terahertz frequencies, we derive an analytical form for the third order microwave/THz susceptibility in graphene which is found to be >103 times larger than that of other typical nonlinear materials. Finally, current and future applications of such properties in THz devices are discussed, in particular, and we discuss a novel application of graphene into active THz filters.
Keywords: Graphene, Nonlinearities, Charge transport properties, Active devices, Filters
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TST, Vol. 6, No. 4, PP. 234-248
(Invited paper) Terahertz spectroscopy study of carrier dynamics and transient photoconductivity in CdSSe nanobelts
Hongwei Liu 1, 2, # , Junpeng Lu 1, #, Minrui Zheng 1, Sing Hai Tang 1, Chorng Haur Sow 1*, and Xinhai Zhang 3*
1 Department of Physics, 2 Science Drive 3, National University of Singapore, Singapore 117542
2 Institute of Materials Research and Engineering, A*STAR (Agency for Science, Technology and Research), 3 Research Link, Singapore 117602
3 Department of Electrical and Electronic Engineering, South University of Science and Technology of China, 1088 Xueyuan Road, Xili, Nanshan District, Shenzhen, Guangdong, China 518055
# These authors make equal contribution to this work.
*1 Email: email@example.com, *3 Email: firstname.lastname@example.org
(Received November 29, 2013)
Abstract: We employ terahertz spectroscopy to investigate the carrier dynamics and transient photoconductivity in ternary CdSxSe1-x nanobelts. The photocarrier density and mobility are extracted by fitting the measured frequency-dependent complex photoconductivities with the Drude-Smith model. Surprisingly, ternary CdSxSe1-x nanobelts are found to exhibit higher photoconductivity than binary CdS and CdSe. This is attributed to higher photocarrier density in ternary compound. In addition, presence of Se in the samples results in prominent CdSe-like TO phonon mode due to electron-phonon interaction. The strength of this mode shows a large drop upon photoexcitation but recovers gradually with time. These results demonstrated that growth of ternary nanostructures can be utilized to alleviate the effects of high surface defects in nanostructures and improve their photoconductivity.
Keywords: Optical pump-THz probe Spectroscopy, CdSxSe1-x nanobelts, Photoconductivity
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TST, Vol. 6, No. 4, PP. 249-257
(Invited paper) Mechanism and applications of weakly ionized plasma terahertz wave detector
Lei Hou, Xiaowei Han, and Wei Shi *
Xi’an University of Technology, Department of Applied Physics, No. 5, South Jinhua Road,
P. O. Box 904, Xi’an, Shaanxi 710048, China
* Email: email@example.com
(Received November 29, 2013)
Abstract: Plasma generated in a discharged neon lamp has been successfully used for terahertz (THz) wave detection. However, the detection mechanisms are disputed. Some researchers advance that the THz wave enhances ionization current, and other researchers propose THz wave enhances diffusion current. We theoretically analyzed the detection mechanism, and found the electrons in the weakly ionized plasma could obtain energy from the incident THz radiation and convert excitation collisions of electrons with excited neutral atoms into ionization collisionsresulting in the increasing of the ionization current. An experiment was designed and testified the mechanism. Some applications of the weakly ionized plasma detector in electromagnetic wave detection and THz imaging were demonstrated.
Keywords: Terahertz wave, Plasma, Detector, Imaging
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