Research On THz-TDS Lock-in Amplifier Technology

The problem of terahertz emission source has been resolved gradually with new materials technology and related disciplines. At the same time, the terahertz wave has a wide range useful value and irreplaceable advantages in many fields, such as spectral field, security field, biochemistry and other fields. So the terahertz technology has got the attention of more and more countries. Terahertz Time-Domain Spectroscopy,(THz-TDS), the earliest technology in the terahertz wave, is the most widely used and effective detection technology with the advantages of wide bandwidth, high detection sensitivity, stable operation at room temperature, etc. Its miniaturization and practical instrument has also become one of the most active areas of current research.This paper studies on the THz-TDS system miniaturized instruments, especially focuses on lock-in amplifier unit of the signal acquisition and processing system. Articles main contents include:1. The basic principle of terahertz wave generating and receiving by photoconductive antenna, the different composition part of terahertz time-domain spectroscopy system and the basic principle of signal detection, the THz' SNR definition, the lock-in amplifier principle, etc.2. This paper creates out a set of lock-in amplifier system on weak photocurrent signal of the THz-TDS system, including current amplifier, programmable narrowband filter, phase sensitive detector, programmable low-pass filter, electronic chopper and other auxiliary units. This system can set the appropriate center chopping frequency, the bandwidth of the narrowband filter, the cut-off frequency of the low-pass filter, the system magnification and other parameters according to different requirements.3. The simulation experiments has been done using this system and the last results of experiments show that this system can detect the 10 u V low frequency sinusoidal voltage signal and the amplitude of the detected signal can reach more than 100 m V. At the same time, this system can also detect the weak low-frequency simulation signals of different center chopping frequencies, different frequencies and different amplitudes.4. The weak photocurrent signal generated by the 8f system of Terahertz Research Center of Tianjin University can be detected successfully in the practical application experiments. The SNR of detected THz wave without loading the sample is about 50 d B,under the moving speed of the optical delay line is 1500um/s and successive scanning.