LASER-MODULATED PHASE-STEPPING DIGITAL SHEAROGRAPHY FOR QUANTITATIVE FULL-FIELD IMAGING OF ULTRASONIC-WAVES

Measurement of surface displacements due to ultrasonic wave propagatio n in elastic solids has traditionally been studied using single-point measurement techniques such as ultrasonic transducers or interferomete rs. Full-field methods, excluding scanning techniques, are uncommon; e xamples include holographic interferometry and Schlieren imaging. In m any cases, these techniques have been used to yield qualitative result s due to inherent difficulties in processing the data. Laser-modulated phase-stepping digital shearography is a full-field, common-path, int erferometric method which can be used to quickly visualize ultrasonic wave fields. A shearography system will be described that provides not only whole-field images of ultrasonic waves, but quantitative displac ement data within these fields. Images are shown of propagating plate and bar waves, and mathematics relating the calculated optical phase t o the ultrasonic wave parameters are presented. (C) 1998 Acoustical So ciety of America.