International Journal of Terahertz Science and Technology
Vol.4, No.2, June 2011. PP.42-70 (4)
date2011-06-30 17:12:32 Click No.3525

TST, Vol. 4, No. 2, PP. 42-45

Temperature Dependence of Terahertz Wave Generation from DAST Crystal Illuminated by 1.56 mm Fiber Laser

Yoshiaki Takemoto, Kei Takeya, Iwao Kawayama, Hironaru Murakami, and Masayoshi Tonouchi*
Institute of Laser Engineering, Osaka University, 2-6,
Yamadaoka, Suita, Osaka, 565-0871, Japan

Takeshi Matsukawa, Yoshinori Takahashi, Masashi Yoshimura, Yasuo Kitaoka, Yusuke Mori and Takatomo Sasaki
Graduate School of Engineering, Osaka University, 2-1,
Yamadaoka, Suita, Osaka, 565-0871, Japan

(Received February 04, 2011; accepted March 29, 2011)

Abstract: 4-Dimethylamino-N-methyl-4-stilbazolium tosylate (DAST) crystal can generate broadband terahertz (THz) wave by optical rectification using femtosecond laser pulses. However, the frequency spectrum of generated THz waves has dips derive from the absorptions of the DAST crystal. We observed temperature dependence of THz wave generation from the DAST crystal. In terms of the frequency spectrum, broad dips at 1.1 and around 4.5 THz at room temperature shift to higher frequency with temperature decreasing, while a small dip at 3 THz shows no temperature dependence.

Keywords: Terahertz, DAST crystal, absorption, temperature dependence

doi: 10.11906/TST.042-045.2011.06.05

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TST, Vol. 4, No. 2, PP. 46-49

THz Radiation from Air Plasma Produced with Aperture-limited Two-color Lasers

H. W. Du1, X. Y. Peng2, K. Y. Zhang1, and Z. M. Sheng1, 3,*
Key Laboratory for Laser Plasmas (Ministry of Education) and Department of Physics, Shanghai Jiao Tong University, Shanghai 200240, China
2Institute of Materials Research and Engineering (IMRE), Agency for Science, Technology and Research (A*STAR), Singapore 117602, Singapore
3Beijing National Laboratory of Condensed Matter Physics, Institute of Physics, CAS, Beijing 100190, China

(Received April 12, 2011; accepted June 10, 2011)

Abstract: Terahertz (THz) radiation from air-plasma produced with two-color femtosecond laser pulses has been measured with controlled pump laser energy by an aperture before the laser focusing lens. It is found that the THz amplitude first increases with the laser energy. With the further increase of the laser energy over 320 mJ, the THz amplitude begins to decrease. This is attributed to the phase-shift between the fundamental pump pulse and its second harmonic along the laser filament, which depends upon the air-plasma length and the corresponding plasma density.

Keywords: Terahertz radiation, Air-plasma, Aperture, Two-color lasers

doi: 10.11906/TST.046-049.2011.06.06

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TST, Vol. 4, No. 2, PP. 50-58

Emission Property of Sc2O3-W Matrix Cathode and Generation of High Current Density Sheet Beams for THz Vacuum Electron Sources

Jinshu Wang*, Wei Liu, Yiman Wang, Meiling Zhou, Tieyong Zuo
The Key Lab of Advanced Functional Materials, Ministry of Education China, School of Materials Science and Engineering, Beijing University of Technology, Beijing 100022, China

(Received August 30, 2010; accepted January 26, 2011)

Abstract: Sc2O3 doped tungsten matrix dispenser cathode prepared by liquid-liquid doping method exhibits high emission property, i.e., space charge limited current density reaches 48 A/cm2 at 850 oCb together with the slope of 1.44 has been obtained. Scanning electron microscope observation shows that the matrix has sub-micrometer microstructure, which is favorable for the diffusion of active substance from the inner part of cathode to the cathode surface. A multi-layer of active substance of Ba, Sc, O formed on the surface of the cathode leads to its conspicuous emission performance. Based on this kind of cathode, rectangular electron beam of 100 m 600 m and square beam of 600 m 600 m have been obtained. A uniformly distributed space charge limited current density of more than 50 A/cm2 can be drawn out from the emitting area at 950 oCb and keeps stable for at least several hundred hours.

Keywords: Scandia doped tungsten, cathode, emission property, shaped beam

doi: 10.11906/TST.050-058.2011.06.07

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TST, Vol. 4, No. 2, PP. 59-70

Terahertz Modulators Based on Silicon P-I-N-Structures in Dielectric Waveguides

V. Grimalsky*, S. Koshevaya, A. Zamudio-Lara, J. Escobedo-Alatorre
Autonomous University of State Morelos (UAEM), Cuernavaca, ZP 62209, Mor., Mexico

(Received March 24, 2011; accepted June 14, 2011)

Abstract: Simulations of the interaction of terahertz (THz) waves with the silicon integrated p-i-n-structures in the isolated silicon dielectric waveguides have been done. The modulation of the fundamental almost linearly polarized electromagnetic mode is considered. This modulation is essential in the case of highly doped p++, n++ regions, which provide the double injection of electrons and holes into i-region. The generalized boundary conditions at the injecting electrodes have been applied in the case of highly doped p++, n++ regions. The silicon dielectric waveguides possess the low losses in the regime without the injection. The investigations of the modulation properties of the integrated p-i-n-structures in the dielectric waveguides of THz range have demonstrated a possibility to use these structures up to the frequencies £8 THz. The transmission and the modulation of picoseconds electromagnetic monopulses have been demonstrated too.

Keywords: Terahertz modulator, Silicon dielectric waveguide, integrated p-i-n-structure

doi: 10.11906/TST.059-070.2011.06.08

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