Digital Speckle Pattern Interferometry (DSPI), originally known as electronic speckle pattern interferometry (ESPI), is
an interferometry based method that allows whole field, non-contacting measurement of microscopic deformation, and
thus exact determination of strain distribution. This paper gives a review of the technique for three dimensional (3D)
deformation and strain measurement with constant and variable measuring sensitivity, and presents the recent
developments for absolute phase measurement. The theory and methodology for the developments are given.
Experimental results are used to demonstrate potentials and limitations for material characterization.
A digital laser microinterferometer with a capability to measure both static and dynamic properties of MEMS (Micro-Electro-Mechanical Systems) and microstructures has been developed. This system is designed to exploit a static and a dynamic measurements of microstructure such as MEMS with either a smooth or a rough surface. The method is based on digital laser Michelson interferometry and digital speckle pattern speckle interferometry (TV - holography) incorporated with optoelectronic devices including a special illumination system, a long distance microscope (LDM), a CCD camera, a high precise phase shifting unit and a signal generator for vibration measurement. The special illumination system can perform both a continuous (for static measurements) and a stroboscopic (for dynamic measurements) illumination by utilizing a Acoustic-Optic-Modulator (AOM). In this paper, the theory and methodology of the digital laser micro-interferometer with the stroboscopic illumination method are described. The usefulness of the micro-interferometer is demonstrated by examples of static and dynamic measurements for different MEMS.
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