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Chapter 3:
Optical Configurations for Measurements Using DSPI
Chapter 2 showed that the variation in optical phase of a speckle distribution can be deterministically related to (a) displacements of the scattering surface, (b) changes in the illumination and observation geometry, and (c) changes in the wavelength of the light source or in the refractive index of the medium through which it travels.1 In cases where the geometry remains constant during the measurement process, as well as the wavelength of the laser light and refractive index, the interferometric configuration is capable of measuring displacement fields produced in the surface of the investigated specimen. Several optical arrangements can be found in the literature that can be categorized as interferometers with sensitivity to either out-of-plane or in-plane displacements. Additionally, there are optical arrangements that are also sensitive to the derivative of displacements; they are known as shearography interferometers.
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