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Illumination systems using photopolymer gratings for speckle interferometry

This study describes the use of diffractive optical elements (DOEs) namely phase gratings, for the simplification of typical illumination schemes employed in digital speckle pattern interferometry. The diffraction gratings are recorded in a photopolymer material that delivers by high diffraction efficiency in transmission but which requires relatively low exposure energies. A significant advantage of this material is that it is completely self-developing, allowing the recording of a custom DOE in-situ and the monitoring of grating efficiency during processing. An example of utilizing this type of DOE in a novel out-of- plane speckle interferometer with what is effectively two- beam illumination is described. A feature of this particular system is the complete insensitivity to in-plane displacement when employing highly off-axis illumination. Incorporation of these DOE's in fiber optic based speckle interferometers allows the realization of simple, compact systems immune to phase and polarization drift.