Study On Key Technology Of Contact Laser Ultrasonic Imaging Based On Opto-acoustic Amplification

In recent years, the laser ultrasonic detection technology has been more and more widely used in industrial non-destructive testing field as a new type of nondestructive testing technology both at home and abroad. Because of the characteristics of wide frequency band, high resolution and high sensitivity, the laser ultrasonic detection technology has become a hotspot in the field of nondestructive testing technology. However, the efficiency of photoacoustic conversion of the thermoelastic effect, which commonly used to inspire laser ultrasonic signal, is too low and difficult to receive in the actual detection. Therefore, the research direction of laser ultrasonic gradually shift to improve the light energy conversion efficiency.In this paper, we designed a set of device based on opto-acoustic effect to improve the energy conversion efficiency without destroying material surface. We did a series of theoretical simulation research of the generating mechanism and opto-acoustic effect by the idea of finite element and finite element simulation software ANSYS. The simulation results proved that the device of OA could promote energy conversion efficiency. On the basis of the theoretical simulation, we designed the transmitting receipting sensor-OA transducer, to realize the function of opto-acoustic effect.Meanwhile, we also built a set of 3D scanning system based on plc control and data acquisition system based on LABVIEW, to evaluate specimen with dynamic scanning method, cooperating with OA transducer. Each component part of the system was introduced detailly in this paper. We used the LABVIEW software to write the defect imaging algorithm and got the image of defects using the data of receiving from specimen. Next, we designed experiments to detect the aluminium plate with different width and depth of defects. The results showed that OA transducer could improve laser energy conversion efficiency and detected defects effectively. And we also could got the information of defect from image of defect, accordancing with the actual results. At the last part of this paper, we summarized the work in this paper and also gave suggestion for the further research study.