Abstract-Dual terahertz comb spectroscopy with a single free-running fibre laser

• Guoqing Hu, 
• Tatsuya Mizuguchi, 
• Ryo Oe, 
• Kazuki Nitta, 
• Xin Zhao, 
• Takeo Minamikawa, 
• Ting Li, 
• Zheng Zheng,  
• Takeshi Yasui, 

https://www.nature.com/articles/s41598-018-29403-9

Dual terahertz (THz) comb spectroscopy enables high spectral resolution, high spectral accuracy, and broad spectral coverage; however, the requirement for dual stabilized femtosecond lasers hampers its versatility. We here report the first demonstration of dual THz comb spectroscopy using a single free-running fibre laser. By tuning the cavity-loss-dependent gain profile with an intracavity Lyot filter together with precise management of the cavity length and dispersion, dual-wavelength comb light beams with slightly detuned repetition frequencies are generated in a single laser cavity. Due to sharing of the same cavity, such comb light beams suffer from common-mode fluctuation of the repetition frequency, and hence the corresponding frequency difference between them is passively stable around a few hundred hertz within millihertz fluctuation. While greatly reducing the size, complexity, and cost of the laser source by use of a single free-running fibre laser, the dual THz comb spectroscopy system maintains a spectral bandwidth and dynamic range of spectral power comparable to a system equipped with dual stabilized fibre lasers, and can be effectively applied to high-precision spectroscopy of acetonitrile gas at atmospheric pressure. The demonstrated results indicate that this system is an attractive solution for practical applications of THz spectroscopy and other applications.

Abstract-Study progess on FET-based Terahertz wave generation and detection

Jin He,  Guoqing Hu,  Zhiping Zhou,   GuangJin Ma,  YanDong He, Mansun Chan,  Lei Song,

http://ieeexplore.ieee.org/document/7998867/

Extensive and much attention have been injected to Terahertz (THZ) technologies in recent years due to its potential application in remote sensing, biomedical, and space communication. Compare with others, FET based THZ devices have a lot of advantages such as frequency tunable, structure compact and room temperature workable. The work in the ULTRA group explored the field effect transistor-based THZ generation and detecting mechanism, simulation tool, compact modeling, size effect, energy band engineering, so to develop the FET-based THZ device physics theory, provide the new simulation tool, build an efficient compact model. The work deliverables will help device scientists and circuit designers deeply understand the pontential and function of the silicon-based FET application in the THZ field, know how to realize the optimized device performance from the fine processing technology and structure design.

Abstract-Measurement of absolute frequency of continuous-wave terahertz radiation in real time using a free-running, dual-wavelength mode-locked, erbium-doped fibre laser

Guoqing Hu , Tatsuya Mizuguchi, Xin Zhao, Takeo Minamikawa, Takahiko Mizuno, Yuli Yang, Cui Li, Ming Bai, Zheng Zheng & Takeshi Yasu

http://www.nature.com/articles/srep42082

A single, free-running, dual-wavelength mode-locked, erbium-doped fibre laser was exploited to measure the absolute frequency of continuous-wave terahertz (CW-THz) radiation in real time using dual THz combs of photo-carriers (dual PC-THz combs). Two independent mode-locked laser beams with different wavelengths and different repetition frequencies were generated from this laser and were used to generate dual PC-THz combs having different frequency spacings in photoconductive antennae. Based on the dual PC-THz combs, the absolute frequency of CW-THz radiation was determined with a relative precision of 1.2 × 10−9 and a relative accuracy of 1.4 × 10−9 at a sampling rate of 100 Hz. Real-time determination of the absolute frequency of CW-THz radiation varying over a few tens of GHz was also demonstrated. Use of a single dual-wavelength mode-locked fibre laser, in place of dual mode-locked lasers, greatly reduced the size, complexity, and cost of the measurement system while maintaining the real-time capability and high measurement precision.