International Journal of Terahertz Science and Technology
Vol.2, No.2, June 2009. PP.39-74 (4)
date2009-06-30 16:54:42 Click No.4809

TST, Vol. 2, No. 2, PP. 39-48

(Invited Paper)On the Problem of Fast Ge:Ga Photodetectors

Michael von Ortenberg1 and Charles H. Mielke2
1Humboldt University at Berlin, Institute of Physics
Newtonstrasse 15, 12489 Berlin, Germany
Email:
orten@physik.hu-berlin.de
2National High Magnetic Field Laboratory
Los Alamos National Laboratory, MPA-NI-NMFL, M/S E536, Los Alamos, NM 87545, USA
Email:
cmielke@lanl.gov

Abstract: We investigate theoretically the response mechanism in Ge:Ga-photo detectors and conclude that only very thin detector elements with thickness of the order 0.1 mm or less obtain reasonably bandwidth of the order of 50 MHz and higher.

Keywords: THz-detector 118.9 µm wavelength, Ge:Ga-detector, fast response

doi: 10.11906/TST.039-048.2009.06.05

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TST, Vol. 2, No. 2, PP. 49-56

High-energy, continuously tunable intracavity terahertz-wave parametric oscillator

Jianquan Yao, Yuye Wang*, Degang Xu, Kai Zhong, Zhongyang Li, and Peng Wang
College of Precision Instrument and Optoelectronics Engineering,
Institute of Laser and Optoelectronics, Tianjin University, Tianjin, 300072;
Key Laboratory of Optoelectronic Information and Technical Science (Ministry of Education),
Tianjin University, Tianjin, 300072
* Tel: 86-22-27407676; Fax: 86-22-27406436; Email:
wangyuye2000@126.com

Abstract: This paper demonstrates an intracavity pumped by a THz optical oscillator from a diode-side-pumped Q-switched Nd:YAG laser. Based on a non-collinear phase matching geometry in the nonlinear crystal MgO:LiNbO3, high-energy, low-threshold, coherent tunable Stokes light is obtained by changing the angles between the resonated idler wave and the pump wave, which means that the widely tunable, high-energy, coherent THz radiation can be generated. The tuning range for Stokes wave is from 1069.4 to 1073.4 nm, corresponding to the THz frequency range of 1.4-2.5 THz. Furthermore, the phenomenon of the coherent tunable second-order Stokes light scattering is also observed.

Keywords: Terahertz generation, nonlinear optics, parametric oscillators and amplifiers, frequency conversion, lasers, diode-pumped.

doi: 10.11906/TST.049-056.2009.06.06

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TST, Vol. 2, No. 2, PP. 57-67

A Dimensionality Reduction Method for THz-TDS Signals via the Recursive Projective Splits Based on PCA

Weixin Xie1,2*, Jihong Pei1, and Jing Li1,2
1Intelligent Information Institute, Shenzhen University, Shenzhen, 518060, China 
2School of Electronic Engineering, Xidian University, Xi¨an, 710071, China
*E-mail:
wxxie@szu.edu.cn

Abstract: Terahertz pulsed imaging delivers THz-TDS signals of a high dimensionality, which raises the difficulties and computations of high dimensional data process. Inspired by the applications of the projective split in ^space time ̄ physics, we apply the projective splits on THz-TDS signals and develop a new dimensionality reduction method for THz-TDS signals. In this method, THz-TDS signals are represented as vectors in a vector space of high dimension. By addition and multiplication, the vector space generates a geometric (or Clifford) algebra of the same dimension. A projective split can factorize the geometric algebra of high dimension into the geometric algebras of lower dimension. Thus, vectors of THz signals in the vector space of high dimension can similarly relate to vectors in the vector space of lower dimension. The projective splits are recursively employed and linearly map the vector space of high dimension into a sequence of sub-spaces step by step. In each step, the Principle Component Analysis (PCA) which explores statistical inherence is performed on vectors in each sub-space, and the homogenous vector of the projective split is determined by the eigenvector of the maximum principal component of PCA. In the vector space of lower dimension, as vectors related to THz-TDS signals from different substances are distant from each other, the application of substance classification and substance identification based on the relative THz-TDS signals can be easily worked out. Experiments are presented and the performance of the method is demonstrated.

Keywords: THz-TDS, geometric algebra, projective splits, dimensionality reduction

doi: 10.11906/TST.057-067.2009.06.07

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TST, Vol. 2, No. 2, PP. 68-74

Low Noise Receivers Using Niobium Nitride Hot Electron Bolometer Mixers from 0.76 to 3.1 THz

J. Chen1*, M. Liang1, L. Kang1, B. B. Jin1, W. W. Xu1, P. H. Wu1,
W. Zhang2, L. Jiang2 and S.C. Shi2
1 Research Institute of Superconductor Electronics (RISE), Department of Electronic Science & Engineering, Nanjing University, Nanjing, 210093, China
2 Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing, 210008, China
* Tel: 86-25-83593717; Fax: 86-25-83593717; Email:
chenj63@nju.edu.cn

Abstract: Low noise receivers using quasi-optical superconducting niobium nitride (NbN) hot electron bolometer (HEB) mixers have been designed, fabricated and measured in the terahertz (THz) frequency range for THz applications in astronomy and cosmology. The NbN HEB mixers consist of a planar complementary antenna and several nanometer (nm) thick NbN bridge connecting across the antenna¨s inner terminals on high-resistivity Si substrates. A double sideband (DSB) receiver noise temperature of 664 K at 0.76 THz, 920 K at 1.6 THz, 1630 K at 2.5 THz and 1710 K at 3.1 THz has been obtained without corrections and no anti-reflection (AR) coating on the surface of the lens.

Key words: Hot Electron Bolometer (HEB) mixer, quasi-optical superconducting heterodyne detector, Terahertz (THz), receiver noise temperature

doi: 10.11906/TST.068-074.2009.06.08

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