Study On Terahertz Time-domain Spectroscopy System With Dual Optical Paths

In recent years,terahertz time-domain spectroscopy(THz-TDS)has received increasing attention all over the world with the rapid development of THz science and technology.A conventional THz-TDS device usually consists a femtosecond laser,a pair of specially designed THz emitter and receiver,and various optical components.Most of THz-TDS devices can only measure THz time-domain spectral signals using transmission mode or reflection mode.In order to measure transmission and reflection signals at the same time,we designed a THz-TDS system with dual optical paths.In addition,we studied the methods for reference signal synchronization of the dual lock in amplifier,adjusting progress of optical path of the system,and improvement of the structure of the system.The results show that the function of simultaneous transmission and reflection measurements has been realized by our system.The innovative work and experimental results of this work are as follows:(1)Based on the conventional spectroscopy technology,the scheme of dual-optical THz-TDS system has been designed and realized for simultaneous transmission and reflection measurements.(2)Two lock-in amplifiers are required in the THz-TDS system with dual optical paths.Therefore we give the method for synchronizing the reference signals of the dual lock in amplifiers.The synchronizing can be realized without external electronic circuits only by fully using the characteristics of lock-in amplifiers.(3)We also studied the structure improvements of dual path THz-TDS,such as the structure of optical delay,THz wave transmission optical path and electro-optical sampling detector.