Research Of Laser-generated Ultrasound For Detecting Vibration

High precision vibration measurement of tiny displacement plays an important role in scientific research and production,it is widely used in material inspection,biomedical engineering and exploration of discipline theory.In the field of vibration measurement,optical measurement method is the most common,it is a kind of high precision,strong stability of non-contact NDT methods.In this paper,we combine laser ultrasonic technology with two wave mixing vibration testing.Because of the photorefractive effect of nonlinear interferometer.The system has a low frequency cutoff,simple structure,high resolution,that make it can achieve high precision measurement of tiny vibration.This article describe the research background,current development and practical application in detail and analyze the photorefractive effect mechanism of photorefractive crystal and two wave coupling characteristics.Then we explain the interference fringes and the energy transfer between two beams caused dynamic grating.At the same time from the experiment we discuss the influence of the incident light intensity,light intensity ratio,beam angle and applied voltage on the two wave coupling strength,to determine the optimal coupling parameters so that the next research.On this basis,we measure the tiny vibration of the piezoelectric ceramics to ensure the feasibility of the two wave mixing vibration interferometer.Then with the advantage of a nondestructive,non-contact,and is not affected by test panel geometry features in laser ultrasound technology.We use Nd:YAG pulsed laser(1064nm)as excitation light source to produce ultrasonic longitudinal wave signal in the artifacts and a two wave mixing interferometer to detect the ultrasonic echo signals.Finally,we successfully measured the thickness and the defect information of the aluminum plate.