Research Of The Laser Ultrasonic Excitation And Detection Technology

As it has small wave length, strong direction, diffract from obstacles, laser has becomingan important research in nondestructive testing field. In this paper, we have researched thelaser ultrasonic excitation and detection technology through simulation and experiment.We have analyzed the key techniques of Laser ultrasonic excitation, which based onLaser ultrasonic excitation mechanism, and designed two kinds of excitation source spatiallymodulated that is point and line focus model. The excitation source of high-power, notcontinuous and invisible features were fully considered. We have used an inverted telescopesystem to improve the beam quality, and then focused by focus point source module. At last,it can output100m-1000m continuously adjustable spot. Line source design wasproposed that is a cylindrical lens and Powell combined with Fresnel lens, the cylindrical lensimaging law was analyzed by optical simulation software, according to its focal results whichshowed a linear Gaussian distribution characteristics, we have proposed a solution that isusing precision diaphragm intercept centralized energy. we have used Solidworks set up amodeled based on Powell linear equations and introduced it to optical analysis software,simulation results show that focused line source have a good uniformity.Optical laser ultrasonic detection theory and practical technical solutions was explored,and a new laser ultrasonic testing system idea was designed. The design using acousto-opticmodulator to introduce a carrier frequency in the signal, using the high frequency modulationmeans to improve the stability of the signal and the anti-jamming ability of the system. Bydouble optical path difference principle to eliminate the influence of ambient noise on theinterference signal; take advantage of polarization characteristics to increase the amplitude ofthe interference signal; by using focus lens group to improve the sensitivity of the system.According to the characteristics of the laser heterodyne signal, we designed phase demodulation module based on AD8302. The module take advantage of AD8302good highfrequency phase measurement and related peripheral circuit design, it solves the problems ofthe traditional circuit system. The theoretical resolution can reach0.1nm, so it achievedhigher precision of laser heterodyne interference signal processing, and the chips can detecttwo interference signal amplitude ratio, so it will monitor the quality of laser heterodyneinterference light path.We have built the laser ultrasonic excitation and detection system, verified the functionof each module by experiment, and has realized the incentive and detection of ultrasonicsignal. The results show that this design can improve the efficiency of laser ultrasonicexcitation, improve the SNR of the ultrasonic testing system, and is conducive to the highfrequency weak laser ultrasonic signal detection.