Digital Speckle Pattern Interferometry (DSPI) with a phase-stepping technique is a whole-field noncontact optical method for quantitative measurement of displacement components at an object's surface. The displacement field is calculated from the optical phase difference caused by the deformation of the object illuminated by a coherent light. Digital image processing algorithms for phase-stepping DSPI have been developed for noise reduction and whole-field strain calculations.

A local phase unwrapping algorithm used in this study permits efficient noise reduction and smoothing of the deformation-induced wrapped phase change map without blurring at 2phi phase edges. Wholefield strain calculation is then performed directly from the wrapped phase change map by the combination of the local phase unwrapping and the least-square surface fitting tec nique. Experimental results from the tilting of a plate were presented to show the effectiveness of the proposed smoothing algorithm. Wholefield displacement and strain distributions were determined for a mechanically fastened joint, achieving a displacement sensitivity of 1/256 and an equivalent strain gage size of 0.4mm. Predictions from a nonlinear finite element analysis were also presented for comparison with the experimental results. Phase-stepping DSPI has proved to be a superior method for whole-field displacement and strain analysis.

The use of laser interferometers for detection of ultrasonic waves in materials is very attractive in those applications that require remote, fully non-contacting inspections. In addition, laser detection allows wide frequency bandwidth sensitivity and accurate determination of the inspection location owing to the small spot size of the interferometer. Ultrasonic waves generated in an aluminum disc by a high power pulsed laser were detected by a Fabry-Perot interferometer, which relies on the laser Doppler effect to detect the motion of the object's surface as changes in the output light intensity. By actively controlling the distance of the two partially reflecting mirrors constituting the Fabry-Perot interferometer, it is possible to keep the detection system at its point of maximum sensitivity. Ultrasonic signals have been detected with signal-to-noise ratios comparable to those of traditionally more sensitive approaches such as piezoelectric or capacitive transducers. Finally, the advantage of same-side generation and detection makes the laser-based ultrasonic system suitable for field inspection or large structures. Ongoing work includes the optimization of non-contact laser based C-scan systems.