Adaptive Holographic Interferometry using Photorefractive Recording Media for Full-field Optical Mapping of Stress and Deformation Fields

Holographic interferometry can be used to measure the stress-field in optically transparent phase objects, as well as to measure the deformation of diffusively scattering opaque objects. The high spatial resolution of holographic interferometry is desirable in situations where the deformation gradients are so high that the resulting high fringe density requires a high-resolution imaging system. However, classical holography has not always been the technique of choice in experimental stress analysis due to the rather cumbersome processing associated with either photographic or thermoplastic recording media. In this paper, we present two adaptive holographic interferometers that use photorefractive BSO crystals as the dynamic reusable recording medium. The first scheme is for deformation measurement on a diffusively reflective opaque aluminum specimen, and the second scheme is a dual-reference beam system for measurement of stress-induced changes in refractive index of a transparent phase object. Both schemes have been implemented in conjunction with phase stepping in order to provide phase maps rather than just fringe patterns. Applications to modal analysis of vibrating plates, and experimental fracture mechanics are demonstrated.