Abstract

Laser ultrasonics [1] offers a technique for nondestructive, noncontact ultrasonic inspection, with the potential for in-factory closed-loop control and quality assurance of the manufacturing process. Progress has been made [1,2,3] which may enable this novel diagnostic to find its way into the manufacturing arena. However, the technology has yet to be cost-effective for most industrial end-users. In particular, the need to compensate for workpiece vibrations, relative platform motion, and optical distortions has driven up the system cost, including active stabilization and costly optics. Compensation techniques including optical phase conjugation [4,5], double-pumped phase conjugation [6,7,8], and two-wave mixing [9,10,11] can potentially enhance the performance of laser ultrasonic diagnostics. These schemes enable wavefront-matching of the beams for efficient coherent detection. However, in some cases, expensive electronic post-processing is required to track out residual mechanical vibrations.

© 1996 Optical Society of America