Adapting the full matrix capture and the total focusing method to laser ultrasonics for remote non destructive testing

Laser Induced Phased Arrays (LIPAs) use post processing to focus and steer the laser generated and detected ultrasonic beam, synthesizing a phased array. The technique is broadband, non-contact, and couplant free, making LIPAs suitable for large stand-off distances, inspection of components of complex geometries and hazardous environments. This paper presents LIPAs synthesized by capturing the Full Matrix (FMC), at the nondestructive, thermoelastic regime. The Total Focusing Method (TFM) is used as the imaging algorithm, where the captured signals are summed with the appropriate time delay, in order to synthesize a focus at every point in the imaging area. The FMC and the TFM, are adapted to the needs of LIPAs in order to enable fast imaging and make more efficient use of the information in the data. Experimental results are presented from nondestructive, laser ultrasonic inspection of an aluminum sample with side drilled holes at depths varying between 10 and 20 mm from the surface