The Polarized Light Based Heterodyne Interference System For The Laser Ultrasonic Signal Detector

The Laser Ultrasonic Detection Technology is a method which makes use of thepulselasertoinspireand detect theultrasonicsignal forrealizingnon-destructivetest.In comparison with the traditional piezoelectric transducer technology, its mostimportant advantage is non-touch detection and elimination of the effect of couplingagent which exists in the traditional piezoelectric transducer technology. Therefore, itis available for various types of complicated sample detection. Moreover, it is a newwideband detection method. Based on it a new type of non-destructive testingtechnologywithgreatprospectofapplicationwillbedeveloped.In order to detect ultrasonic signals better, the traditional heterodyneinterferometerisimprovedbyusingalinearlypolarizedlightasthelightsource;andadiaphragm to eliminate the optic noises and the influences of the feedback lights onthe light path. The first order light is used as the reference. A laser heterodyneinterferometersystemwhichissimpleinstructureandeasytoadjustisdesigned.Niceheterodynesignalshavebeenobtained.Aphase sensitive detection circuit is designed to demodulatethe ultrasonic signal.The phase variation can be calculated by multiplying the amplified signal with thereference interferometric signal. Experimental results show that quite nice ultrasonicsignalscanbeobtainedafterfiltering.The measured results and the associated source errors are analyzed, and methodsfor reducing these errors are discussed. An approach for further study on theinterferencesignalsisproposed.The successful detection of the signal generated by the ultrasonic probes showsthatthedevelopedsystemcanbeusedforlaserultrasonicdetection.