Research on Variable Angle Fiber-Type Terahertz Time-Domain Spectrometer
LI Zheng1,2, SUN Qing2*, FENG Mei-qi2, SHANG Liang1, DENG Yu-qiang2, LI Chao-chen2
1. School of Physics and Physical Engineering, Qufu Normal University, Qufu 273165, China
2. Division of Optics, National Institute of Metrology, Beijing 100029，China
Abstract：Terahertz time-domain spectroscopy (THz-TDS) technology is widely used in many fields such as material composition identification, explosive detection, drug and drug composition analysis, and medical diagnosis. The traditional THz-TDS uses a Ti: sapphire femtosecond laser as a light source, which is bulky and costly, and limits the large-scale application of THz-TDS. Using a fiber femtosecond laser combined with a fiber-coupled terahertz photoconductive antenna, the THz-TDS system can be designed to be very compact and flexible, while eliminating the need for a free-space optical path, greatly reducing the number of optical mounts The influence of external environment on the signal such as vibration has great application potential in industry and in the field. In this paper, a fiber-type THz-TDS system is designed and developed, and the three subsystems of optics, electricity and software are briefly introduced. The femtosecond pulse width is controlled by fiber dispersion management, so that the femtosecond pulse width of the terahertz photoconductive antenna is kept at about 50 fs, thereby eliminating the terahertz time domain pulse broadening caused by femtosecond pulse broadening. By precisely controlling the polarization state of the femtosecond laser, the polarization direction of the pump laser and the detection laser is kept parallel with the fast or slow axis of the polarization maintaining fiber, thereby eliminating the splitting phenomenon of the terahertz time domain pulse and obtaining the signal to noise ratio. Better than 12 000 single-pulse terahertz time domain waveforms. The variable angle optical path structure design enables easy switching of terahertz transmission spectrum measurement and reflection spectrum measurement, as well as the measurement of variable angle terahertz spectrum.
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