Displacement measurements in the interior of 3-D bodies using scattered-light speckle patterns

Two new techniques making use of the scattered light speckle pattern have been developed which yield the displacements on an arbitrary interior plane of a 3-D body. When a sheet of coherent light passes through a transparent 3-D body, a small fraction is scattered. This scattered light produces a speckle pattern in an imaging system. By recording two superimposed images of this speckle pattern, one before and one after body deformation, the displacements on the interior illuminated plane can be found. The technique of scattered light photography uses a single illuminating beam and is sensitive to displacements greater than one speckle diameter. Scattered light speckle interferometry uses two illuminating beams and is sensitive to displacements greater than one half the wavelength of light being used. With both techniques, the double exposed speckle photograph is optically processed to yield displacement information.