International Journal of Terahertz Science and Technology
Vol.6, No.3, September 2013. PP.165-211 (5)
date:2013-09-30 09:28:52 Click No.:2305

TST, Vol. 6, No. 3, PP. 165-176

Nonlinear interaction of terahertz and optical waves in nitride films

V. Grimalsky *, S. Koshevaya, M. Tecpoyotl-T., and J. Escobedo-A.
Autonomous University of State Morelos (UAEM), Cuernavaca, ZP 62209, Mor., Mexico
* E-mail:
v_grim@yahoo.com

(Received April 03, 2013)

Abstract: It is considered the three-wave interaction between a space charge wave and two counterpropagating electromagnetic waves of terahertz or optical ranges in waveguides based on n-GaN or n-InN films. The waveguides are formed by the nitride films placed on a dielectric substrate. Space charge waves at the frequencies f£  500 GHz are amplified due to the negative differential conductivity, their finite widths lead to decrease of the amplification. It is possible to obtain amplification of the electromagnetic wave ~30 dB at the distances £ 100 mm. The input electromagnetic pulses of the durations ³100 ps can be amplified by the three-wave interaction without distortions when the transverse width of the pulse is greater than 5 mm.

Keywords: Negative differential conductivity, n-GaN, n-InN films, Three-wave interaction, Amplification of THz and optical pulses

doi: 10.11906/TST.165-176.2013.09.10

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TST, Vol. 6, No. 3, PP. 177-182

Evaluating graded doping profiles of single domain GaN gunn diodes for THz applications

Smita Francis *, and Robert van Zyl
Cape Peninsula University of Technology, French South African Institute of Technology, Department of Electrical Engineering, Symphony Way, Bellville, 7535, South Africa.
* Email:
sfrancis@polytechnic.edu.na

(Received March 02, 2013)

Abstract: The microwave performance of a single domain GaN Gunn diode is investigated using the Monte Carlo particle simulation technique. The simulations show that the performance of the diode is enhanced by appropriate engineering of the transit region doping profile. Three doping profiles are considered, namely flat, exponentially increasing and exponentially decreasing towards the anode. Improved microwave performance is obtained with the increasing doping profile, yielding 728 mW at a fundamental frequency of 0.175 THz, and 36 mW at the third harmonic of 0.525 THz. The simulations suggest this to be approaching the operational frequency limit of the device. Thermal effects are incorporated consistently with charge evolution through the device.

Keywords: Gunn diode, Negative differential resistance, Monte Carlo Simulation, Graded transit region

doi: 10.11906/TST.177-182.2013.09.11

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TST, Vol. 6, No. 3, PP. 183-188

A sub-THz Mach-Zehnder quadruplexer

L.Lubyako 1* and W. A. Bongers 2
1
Institute of Applied Physics RAS, 603950, Nizhny Novgorod, Russia,
2 DIFFER (Dutch Institute For Fundamental Energy Research). PO Box 1207, 3430 BE Nieuwedein, The Nether-lands
W.A.Bongers@differ.nl
*1 E-mail: lub@appl.sci-nnov.ru

(Received  January 09, 2012)

Abstract: The paper describes a multi-port, multi-frequency, quasi-optical device capable to combine four incident waves and to switch the combined wave flow from one output channel to another by control of input wave frequen-cies.

Keywords: Quasi-optic, Diplexer, Mach-Zehnder interferometer.

doi: 10.11906/TST.183-188.2013.09.12

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TST, Vol. 6, No. 3, PP. 189-205

Theoretical analysis and simulation of growth rate and start current in Smith–Purcell free-electron lasers

D. Li 1*, M. Hangyo 2, Z. Yang 3, Y. Tsunawaki 4, Y. Wei 3, Y. Wang 3, S. Miyamoto 5, M. R. Asakawa 4, and K. Imasaki 1
1
Institute for Laser Technology, Suita, Osaka 565-0871, Japan
2 Institute of Laser Engineering, Osaka University, Suita, Osaka 565-0871, Japan
3 School of Physical Electronics, University of Electronic Science and Technology of China, Chengdu 610054, China
4 Department of Pure and Applied Physics, Faculty of Engineering Science, Kansai University, Osaka 564-8680, Japan
5 Laboratory of Advanced Science and Technology for Industry, University of Hyogo, Ako, Hyogo 678-1205, Japan
*1 Email:
Dazhi_li@hotmail.com

(Received March 08, 2013)

Abstract: We present an analytical theory for small-signal operation of a Smith–Purcell free-electron laser with a finitely thick electron beam travelling close to the surface of a grating. The dispersion equation is derived from a self-consistent set of small-signal equations describing the dynamics of beam-wave interaction. Through the analysis of the power flow above the grating, the mechanism of beam-wave interaction in the device is explored. By solving the dispersion equation carefully, we reveal that the growth rate of the field amplitude holds a finite value at the Bragg point, which is different from previous theoretical predictions. After deriving an approximate equation to calculate the growth rate, the oscillation start current of the device is worked out by considering the power flow above the grating. The predictions of our theory are compared with those of particle-in-cell simulations, and the agreement is reasonable.

Keywords: Smith–Purcell free-electron laser, Growth rate, Start current, Particle-in-cell simulation

doi: 10.11906/TST.189-205.2013.09.13

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TST, Vol. 6, No. 3, PP. 206-211

Cross-Phase modulation of laser pulses by strong single-cycle terahertz pulse

Nan Yang 1, Hai-Wei Du 2*
1
Laboratory for Laser Plasmas (Ministry of Education) and Department of Physics,
Shanghai Jiaotong University, Dongchuan Road 800, Shanghai 200240, China
2 Terahertz Sensing And Imaging Team, Advanced Science Institute, RIKEN, 519-1399 Aramaki-Aoba, Aoba-ku, Sendai, Miyagi 980-0845, Japan
*2 Email:
haiweidu@yahoo.com

(Received January 17, 2013)

Abstract: Laser pulses cross-phase modulated by strong single-cycle THz pulse is investigated numerically. It is found that the cross-phase modulation is mainly induced by Pockels effect and Kerr effect. These effects can make the laser pulses spectral shift, including red-shift and blue-shift, and broadening. And the duration of the THz pulse affects the cross-phase modulation greatly.

Keywords: Cross-phase modulation, THz pulse

doi: 10.11906/TST.206-211.2013.09.14

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