The System Of Orthogonal Polarization Differential Interferometer To Detect The Surface Acoustic Waves

It is an important research direction of surface acoustic waves(SAWs)detection technology to characterize the mechanical properties of precision machined surfaces by using the dispersion curve of surface acoustic waves to determine the Young's modulus of the material.Generally,the propagation velocity of the surface acoustic wave in the isotropic homogeneous medium remains constant,while the atomic arrangment order of surface and subsurface have been changed by the machined process,which affects the propagation velocity.Based on this principle,this paper aims to develop a surface acoustic wave detection system based on optical interference,which provides a good experimental equipment for the surface and subsurface defects detection.Firstly,the development of excitation and detection SAW at home and abroad is researched.The detection system in this paper,non-contact orthogonal polarization differential interferometer is determined by comparing with several different detetion methods.Secondly,the detection principle is deduced by Jones matrix of the polarizing optical components,which is used to lay the theoretical foundation for the selection of laser and detector.The components are determined,especially for the power of HeNe laser and the minimum photographic power of the balanced detector.The minimum detection displacement of the system was determined to be 1.2nm according to the laser wavelength and oscilloscope accuracy.Then the interferometer system is built,debugged and calibrated.The system is debugged from the aspects of the power loss of each optical element,the relationship between the visibility of the interference ring and the light intensity ratio between detection and reference,and the system noise.The standard sine wave and stepped displacement signals are used to calibrate the interferometer,and the minimum response of the interferometer to the dynamic input and the static input is observed by using piezoelectric ceramics.The calibration results show that the minimum dynamic input response is 3 nm and the minimum static input response is 25 nm.Finally,compared with the PVDF piezoelectric thin film system,the spectral bandwidth of the SAW signal on monocrystalline silicon and aluminum detected by the interferometer system is improved by 20 MHz.The SAW signal is collected several times in the same position on the aluminum sample to calculate the repeatability error of the system,which is 1.255%,according to the peak-to-peak value.The influence of sample surface roughness on the phase velocity of SAW is investigated by using PVDF piezoelectric thin film SAW detection system,which not only provides a guide to the choice of surface roughness,but also provides a new idea for the roughness detection.