Yan Zhang

Guest Editorial TTA Special Section on Terahertz Spectroscopy

Yan Zhang

Terahertz (THz) radiation has many potential applications in communication, homeland security, safety inspection, sensing, and imaging. Spectroscopy may be the most fundamental application of the THz radiation. The wide spectrum of the THz pulse makes it much easier to obtain the spectra of materials with many absorption peaks, which related with the samples directly. This feature absorption peaks are called finger spectra and can be used to identify the object. Both amplitude and phase information achieved with the time domain spectroscopy (TDS) allows to extract more parameters of the measured materials. If both transmission and reflection spectra of a sample can be precisely achieved, all electromagnetic parameters, including permittivity and permeability of the materials, can be determined. It was found that many materials such as the illegal drugs, explosives, biological macro-molecules, cosmetics, fine chemical materials, edible pigments, food additives, homocysteic acid, heavy ions in soil, Chinese medicines, tobacco, crops, the oil, carbon nanotubes, superconductors, semiconductors, and their heterojunctions, have finger absorption peaks in the THz range. It is expected that the THz spectroscopy can be used for materials identification and quality control.1

In this special section, several progresses in the THz spectroscopy are reported, including the development of THz TDS system, application of THz spectroscopy for investigation of explosive, and using the emission spectrum for THz photoconductive antennas improvement.

In the first paper, the THz-TDS system and the related technology used in the Capital Normal University are described in detail. Some works based on this homemade system are summarized, which shows the applications of the THz-TDS, especially in the area of identification of illegal drugs and explosives.

In the second paper, a detail investigation of absorption spectra of the RDX with different granularity is presented. The characteristic absorption peaks of samples were acquired in the spectral region from 0.1 THz to 2.5 THz using the THz-TDS. All samples have similar absorption peaks around the frequency of 1.05 THz, 1.30 THz, 1.46 THz, 1.65 THz, and 1.95 THz. The theoretical calculation based on the density functional theory at a BP/DNP level is also carried out to identify the measured absorption peaks. The origin of the absorption peaks is assigned. This work shows that the particle size of the sample can affect its THz spectra, but the inherent absorption peaks cannot be affected.

The third paper investigates the emission spectrum of the THz photoconductive antennas with improved electrode structures. The emission spectrum is a powerful method in the investigation of the superconductors, semiconductors, and their heterojunctions. In this work, the effect of the electrode structure on the emission spectrum is studied. An amplitude increase of about 40% is experimentally observed for the terahertz signals generated from the optimized structures. This work shows the feasibility of developing highly efficient THz photoconductive emitters by optimizing the electrode structure.

As the guest editor of this issue, I would like to express my sincere thanks to all the authors for their generous contributions to this special section, they have shared their newest works and exciting results with us. I also appreciate the assistance of the editorial staff, their great efforts make this special section to be pressed in time.Yan Zhangreceived his M. S. degree and Ph.D. degree from Harbin Institute of Technology and Institute of Physics, Chinese Academy of Science in 1996 and 1999, respectively. He is now a full professor with the Department of Physics, Capita l No rmal Univer sity. He has publishedmorethan150journalpapers.His research interests include optical information processing, surface plasmoic optics, and THz spectroscopy and imaging. He was the recipient of the New Century Excellent Talents Program Award from the Ministry of Education of China.

Yan Zhang,Guest EditorCapital Normal University Beijing, China

Digital Object Identifier: 10.3969/j.issn.1674-862X.2014.02.001