Laser generation of focused ultrasonic wave

An arc-shaped line array slit is used for the laser generation of focused laser-ultrasonic wave. The spatially expanded Nd:YAG pulse laser is illuminated through the arc-shaped line array slit on the surface of a sample to generate the ultrasonic wave of the same pattern as the slit. Then the generated ultrasonic wave is focused at the focal point of which distance from the slit position is dependent on the curvature of the slit arc. The relationship between the characteristics of the generated ultrasonic wave, including the focusing performance and several design parameters, such as slit width and slit interval, are investigated. By using the focused wave we can upgrade the inspection ability for the small size defect with the improvement of spatial resolution.