Research On Laser-generated Surface Acoustic Wave Detection System Based On Michelson Interference Technique

The continuous progress of science and technology has been promoting the rapiddevelopment of non-destructive testing techniques. As a branch of non-destructivetesting technique, surface acoustic wave detection technique with its uniqueadvantages is favored by the majority of researchers. Researching it and applying it toindustry field have important significance and value.At present, laser excitation technique is widely used for laser surface acousticwave generation, it not only can be used in solid, liquid and gas samples, but also caninduce surface acoustic waves have enough amplitude, which make this technique hasobvious advantages than other techniques. However, there are many surface acousticwave detection techniques, mainly including atomic force microscope technique,piezoelectric sensor technique, light defection detection technique, interferometerdetection technique, and differential confocal technique, where the first two arecontact detection techniques that bring pollution even damage to the sample surface.The light deflection detection system uses oblique incident/reflection configuration,which results in big proliferation and poor focus point, making the system has lowmeasurement precision. There are several interferometer techniques, for example,Fabry-Perot interferometer technique, Heterodyne interferometer, Michelsoninterferometer technique and so on, but the first two techniques have narrowmeasurement bandwidth, affecting measurement precision. Differential confocaldetection technique needs stability and measurement bandwidth improvement.Because surface acoustic wave signals are very weak, moreover, their amplitudesdecay exponentially with the depth they go into materials. Therefore, in order toachieve precise detection, technique with high sensitivity is needed. Among thetechniques described above, Michelson interferometer technique has the advantagesof non-contact, non-destructive, high sensitivity and wide measurement bandwidth,which is greatly suitable for surface acoustic wave detection. This paper is committedto the study of Michelson interferometer surface acoustic wave detection technique toachieve precise detection of surface acoustic waves on sample surface.The main works of this paper are as follows: 1. Reviewed the state-of-the-art of surface acoustic wave detection techniques,summarized the existing problems, and cleared the research content.2. Established the simulation function of surface acoustic wave, and applied it forANSYS simulation of surface acoustic wave propagation on sample surface withmicro-defects, verifying the possibility to use surface acoustic wave formicro-defect detection. Meanwhile, developed the dispersion curve calculationalgorithm.3. Tested and analyzed experiment instruments of different types, especially pulselasers, He-Ne lasers and balanced photo-detectors, and finally determined the bestequipments for the going on of the experiment.4. Constructed the light deflection system to detect laser surface acoustic waves, andsuccessfully confirmed the existence of them. Then, designed and constructed theclassical and polarized Michelson Interferometer, and conducted surface acousticwave detection and experiment result analysis.5. Conclusion and future work. Summarized the work of the thesis, presented thepoints need improvement in classical and polarized Michelson Interferometersurface acoustic wave detection systems, and proposed recommendations.