TST, Vol. 7, No. 4, PP. 160-171
(Invited paper) The physics of and prospects for THz-Compact FELs
Gian Piero Gallerano *, Andrea Doria, and Emilio Giovenale
ENEA - Radiation Sources Laboratory – 00044 Frascati, Italy
* Email: gianpiero.gallerano@enea.it
(Received December 15, 2014)
Abstract: In this paper we review the physics of long wavelength Free Electron Lasers (FELs) driven by low-energy electron accelerators. We show how the waveguide operation can lead to new attracting features, like a wide gain bandwidth, a short resonator length, and the possibility of generating sub-picosecond radiation pulses in compact table-top devices. The short electron pulse duration associated with radio-frequency (RF) accelerators also gives rise to the so-called "coherent spontaneous emission", which greatly enhances the performance of this type of sources.
Keywords: Terahertz sources, Free electron lasers, Coherent synchrotron radiation.
doi: 10.11906/TST.160-171.2014.12.15
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TST, Vol. 7, No. 4, PP. 172-180
(Invited paper) Terahertz silicon lasers based on intracenter impurity transitions
H.-W. Hübers 1, 2*, S. G. Pavlov 1 , R. Kh. Zhukavin 3, and V. N. Shastin 3
1 German Aerospace Center (DLR), Rutherfordstr. 2, 12489 Berlin, Germany
2 Humboldt-Universität zu Berlin, Newtonstr. 15, 12489 Berlin, Germany
3 Institute of Physics of Microstructures, Russian Academy of Science, 603950Nizhny Novgorod, Russia
*2 Email: heinz-wilhelm.huebers@dlr.de
(Received December 15, 2014)
Abstract: The first silicon laser was reported in the year 2000. It is based on impurity transitions of the hydrogen-like phosphorus donor in monocrystalline silicon. Several lasers based on other group-V donors in silicon have been demonstrated since then. These lasers operate at low lattice temperatures under optical pumping by a mid-infrared laser and emit light at discrete wavelengths in the range from 250 to 50 µm (1.2 THz to 6.9 THz). Dipole-allowed optical transitions between particular excited states of group-V substitutional donors are utilized for donor-type terahertz (THz) silicon lasers. Population inversion is achieved due to specific electron-phonon interactions inside the impurity atom. This results in long-living and short-living excited states of the donor centers. The frequency of the laser can be tuned by applying an external magnetic field or by applying a compressive force to the laser crystal. Another type of the THz laser utilizes stimulated resonant Raman-type scattering of photons by a Raman-active intracenter electronic transition. By varying the pump laser frequency, the frequency of the Raman intracenter silicon laser can be continuously changed between at least 4.5 THz and 6.4 THz. Recently lasing from p-type boron-doped silicon has been obtained. In addition, fundamental aspects of the laser process provide new information about the peculiarities of electronic capture by shallow impurity centers in silicon, lifetimes of non-equilibrium carriers in excited impurity states, and electron-phonon interaction.
Keywords: Terahertz, Silicon, Laser, Donor, Impurity, Raman
doi: 10.11906/TST.172-180.2014.12.16
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UCMMT candidates for best student papers
TST, Vol. 7, No. 4, PP. 181-187
A High harmonic large orbit gyrotron in THz range
Xiang Li *, Jiandong Lang, Yasir Alfadhl and Xiaodong Chen
School of Electronic Engineering and Computer Science
Queen Mary University of London
Mile End Road, London, United Kingdom, E1 4NS,
* Email: xiang.x.li@qmul.ac.uk
(Received May 31, 2014)
Abstract: A high-harmonic large orbit gyrotron (LOG) operating in the THz range has been designed and studied. Numerical simulations have shown that the 5th harmonic oscillation at 283 GHz can be selectively excited by proper choice of the external magnetic field and the electron beam current. The high harmonic operation of LOG is characterised by the considerable reduction of the required external magnetic field strength. The beam-wave interaction, the starting oscillation process and the ohmic loss of the designed LOG are also examined. The analysis procedure and the conclusion can form the basis for the study of even higher harmonics operation.
Keywords: Gyrotron, Harmonic resonance, Large orbit gyrotron (LOG), THz range.
doi: 10.11906/TST.181-187.2014.12.17
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TST, Vol. 7, No. 4, PP. 188-192
Searching the start oscillation conditions of gyrotron backward wave oscillator using particle swarm optimization
Qiu-Shi Wang *, Ji-Run Luo and Shu-Yuan Peng
Key Laboratory of High Power Microwave Sources and Technologies, Institute of Electronics,
Chinese Academy of Sciences,
Beijing 100190, People’s Republic of China
* Email: qiushiwork@gmail.com
(Received May 31, 2014)
Abstract: Particle swarm optimization (PSO) is used to search the start oscillation conditions of gyrotron backward wave oscillator (gyro-BWO), the results are more accurate than the original algorithms.
Keywords: Gyro-BWO, Oscillation conditions, PSO
doi: 10.11906/TST.188-192.2014.12.18
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TST, Vol. 7, No. 4, PP. 193-197
Equivalent circuit method of π-mode frequency of rising-sun magnetron
Song Yue 1*, 2, Zhao-chuan Zhang 1, and Dong-ping Gao 1
1 Key Laboratory of High Power Microwave Sources and Technologies, Institute of Electronics,
Chinese Academy of Sciences, Beijing 100190, China
2 University of Chinese Academy of Sciences, 19 BeisihuanXilu, Beijing 100049, China
*1 Email: yuessd@gmail.com
(Received May 31, 2014)
Abstract: In this paper, equivalent circuit method is adopted to investigate π-mode frequency of rising-sun magnetron theoretically. The equivalent inductance and capacitance of resonant cavities are calculated with structure dimensions, and then π-mode frequency is obtained. Theoretical results are consistent well with that of simulations.
Keywords: Rising-sun magnetron, Π-mode, Equivalent inductance, Equivalent capacitance
doi: 10.11906/TST.193-197.2014.12.19
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TST, Vol. 7, No. 4, PP. 198-201
Microwave window design for 90 GHz-100 GHz TWT
Gangzhang *, Zongfei Jin, Huarong Gong, Tao Tang and Yubin Gong
National Key Laboratory of Science and Technology on Vacuum Electronics
University of Electronic Science and Technology of China, Chengdu, Sichuan, China, 610054
* Email: zhgang1314@sina.com
(Received May 31, 2014)
Abstract: This paper mainly discusses 90 GHz-100 GHZ pillbox window whose window chip uses sapphire for TWT. We simulated and optimized it by HFSS, and the result shows that the VSWR of the two kinds of windows are less than 1.27, and the second kind of the window uses bigger cylindrical wave guide which can make it easer to process than the first kind. We made the first kind of window, and tested it.
Keywords: Pillbox window, VSWR, Sapphire, THZ.
doi: 10.11906/TST.198-201.2014.12.20
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TST, Vol. 7, No. 4, PP. 202-206
Design for w-band folded waveguide traveling-wave tube
Zongfei Jin, Gang Zhang, Tao Tang, Huarong Gong *, Chun Wang, Bin Wang, and Yubin Gong
National Key Laboratory of Science and Technology on Vacuum Electronics
University of Electronic Science and Technology of China, Chengdu, Sichuan, China, 610054
* Email: hrgong@uestc.edu.cn
(Received May 31, 2014)
Abstract: This paper designs a folded waveguide traveling wave tube which works in 97 GHz-99 GHz. The interaction efficiency of the whole working band is about 3%, and the output power is up to 57 w, therefore the whole tube gain is more than 37 dB. The high-frequency characteristics of the slow wave structure and the amplification performance of the TWT have been investigated.
Keywords: W-band, Folded waveguide, Traveling wave tube.
doi: 10.11906/TST.202-206.2014.12.21
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