Laser ultrasonic probe for industrial or high-temperature applications

Ultrasonic nondestructive testing is typically used for location and sizing of internal and surface defects or for measuring material properties. Traditional techniques use contacting transducers, which are difficult to implement for on-line quality control or high temperature applications. Because laser ultrasonic (LU) systems are non-contacting, they can be used for testing moving specimens or for operation in hazardous environments.; One of the most promising applications for LU inspection systems is high temperature testing. Fundamental LU research was performed to investigate the effects of specimen temperature on the generation and propagation of ultrasound. Results include ambient and elevated temperature measurements of on-epicenter sound pressures and directivity patterns. Numerical modeling for refraction through a temperature gradient is also included.; In order to enhance bulk wave generation, a phased array was designed and constructed using optical fiber bundles. Because the fibers are fragile, a fiber containment ring was developed. The phased array can be used with a focusing objective to obtain a variety of beam steering angles. Depending on the application, the system can be calibrated to use either thermoelastic or ablative sources. This work includes the first implementation of an ablative phased array. Results include theoretical analysis of ablative phased arrays and experimentally obtained directivity patterns for thermoelastic, transition and ablation sources.; LU inspection systems using optical fiber delivery are highly versatile. Introduction of a distal-end, focusing objective into the optical fiber delivery system increases the allowable working distance between the optical fiber(s) and test specimen. The focusing objective permits strong generation, using material ablation as the generating mechanism. This work includes the design and testing of two focusing objectives. Results include experimentally obtained directivity patterns demonstrating ultrasonic generation using thermoelastic and/or ablation sources. Use of a distal-end, focusing objective for laser-fiber ultrasonic NDT is unique to this work.; The industrial application highlighted in this work is weld monitoring and quality control. Because the LU probe generates strong signals and is non-contacting, flexible and physically robust, it a practical solution for industrial ultrasonic inspection applications. When used in the phased array configuration, the laser probe is particularly suited for the weld control application featured.