Phase-shifting dynamic holographic interferometry using BSO photorefractive crystals

Holographic interferometry of phase objects as well as diffusely scattering opaque specimens is achieved in quasi real-time using two-wave mixing in photorefractive Bi ₁₂SiO₂₀ (BSO) crystals. In the case of diffusely scattering specimens, phase shifting holographic interferometry of a vibrating plate specimen is done by recording at least 3 double pulse holograms with different phase shifts of the reference beam. The good signal-to-noise ratio and resolution of the resulting holographic interferograms enable phase measurement of complex vibration modes. Quasi-heterodyne interferometry is also demonstrated for phase objects under non-recurring loading. A double exposure hologram with two separate reference beams at different incident angles for the two exposures is recorded in a BSO crystal. The two recorded object states are subsequently reconstructed by the reference beams at any desired phase by simply introducing a relative phase shift between the two readout reference beams. Because of the speed of the photorefractive effect and the lack of need for post processing, such a recording material allows image acquisition comparable in temporal resolution to electronic speckle techniques with the image quality of classical holography.