Study On New Lock-in Amplifier Technology About The Signal Of Practical Thz Spectrometer

THz-TDS technique is a coherent measurement technique with broadband THz pulse. It can simultaneously detect the amplitude and phase information of THz pulse and the spectral information can be achieved by Fourier transform. Besides, it is one of the latest means of the spectrometric detection, which has important applications in many areas of basic research. However, at present, there is no commercialized product based on THz-TDS technique in China. Therefore, It is an event of significance to develop the high power, miniaturized and practical products with THz-TDS technique. From the perspective of the practicability of the THz-TDS system, this paper has proposed a new program about the acquirement of THz pulse signals instead of the former lock-in amplifier, which is not conducive to integration because of its great size.Concrete research content of this paper includes the following several aspects:1. According to the principle of the existing acquisition system of Terahertz time domain spectroscopy signal, a new acquisition program of terahertz pulse has been put forward.2. One type of lock-in amplifier circuit based on CD552-R3 has been designed, which is based on the analysis of theory of weak signal detection and lock-in amplifier technology combining with the characteristics of the practical acquisition signals. The design of the circuit mostly includes two parts: the design of phase sensitive detection circuit and preprocessing circuit. And also the property of the circuit has been tested. The test result shows that the phase sensitive detection circuit does well in the distinguish of the amplitude and phase and the linear correlation coefficient is above 0.999. Besides, the magnification of the system is 100000 times and the linear relativity of the whole system is above 0.999.3. The acquisition experiments of THz pulse have been carried out with the lock-in amplifier circuit which is based on CD552-R3. The result shows that the THz voltage signal which is at microvolt level can be tested from the noise which is at mill volt level. Compared with the experiments with lock-in amplifier SR830, the circuit with CD552-R3 can match for it in raising signal-to-noise ratio and reach the purpose of the circuit design.4. The repeatability experiment of CD552-R3 lock-in amplifier circuit has been done, and its stability and dependability have been analyzed, at the same time the deviation of the system also has been calculated and analyzed.