A whole-field speckle strain sensor is presented. The speckle strain sensor allows the measurement of all three in-plane components of the strain field simultaneously without touching the surface of the sample. The strain fields are extracted from the in-plane motion of defocused laser speckles in a telecentric imaging system. To distinguish the contribution to the speckle motion from surface translation, rotation, and strain, the speckle motion from three lasers with different illumination directions and wavelengths has to be analyzed separately. Simultaneous acquisition of the three individual speckle patterns is achieved by means of splitting the light from the lasers onto separate but synchronized detectors with the aid of dichroic mirrors. The motion of the speckles is calculated with digital speckle photography (speckle correlation), which enables the strain sensor to measure strain fields with noise levels as low as 10 mustrain. (C) 2002 Optical Society of America. [References: 11]
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