Study On Vibration Detecting Technology Of Laser Doppler

With the rapid development of modern engineering and technology, especially in the area of aviation, spaceflight and machine produce, it's necessary to make high accuracy vibration measurement. Especially, in the domain of physical geography probe, seism probe has become the most effective and widely used method, which can be used in probing petroleum mineral resources, coal, terrestrial heat, engineering geology and hydrological geology. Therefore, it's important to acquire and process vibration signals, differentiate and analyze the system, control the vibration and noise. After comparing many vibration detecting methods, considering that the Laser Doppler method has many advantages such as high accuracy, rapid dynamic response, large measuring range, non-contact, resisting electron-magnetic interference, avoiding landscape orientation interference, it is selected to detect vibration in this paper.The works of this paper is one part of the project "research on method and theory of Laser Doppler effect detecting seism wave". Based on the applied domain of the project, the measurement of signal with vibration frequency range from 2Hz to 10Hz has been studied. The following results are achived:1. Theory of the measurement of vibration using Laser Doppler effect are researched and differential Laser Doppler optical system are designed. Especially, acousto-optic modulator is used in this system, which can improve the signals' SNR and anti-jamming ability of the optical system.2. According to speckle principle, Relation between intensities of laser Doppler signals and structure parameters of optical system is analysed. Based on Gauss beam theory and characteristic of vibration detecting, the parameters of the optical system are optimized, which has improved the system's resolution and SNR.3. Lock-in amplifier is researched to detect weak signals, and NI's DAQ card are used to acquire data. The adjustment of the whole system, acquisition of data and analysis of experiment data are completed. In the end, the software method is applied to get amplitude and frequency parameters of vibration.