Polarization properties in two wave mixing with moving grating in photorefractive BSO crystals. Application to dynamic interferometry

The polarization properties of the volume gratings in photorefractive B ₁₂SiO ₂₀ crystals permit to increase the contrast and signal to noise ratio in the image plane of a large size vibrating object structure. The experiment is based on the nearly degenerate two wave mixing of a pump beam with a low intensity signal beam due to the object structure (moving grating recording with an externally applied field in the 110 crystallographic direction). For a correct orientation of the incident recording beam polarizations, the pump beam emerging from the crystal is linearly polarized, while the signal, after two beam coupling is elliptically polarized. The selective attenuation of the direct pump and scattered beams is obtained with a polarizer. Improved contrasts in the interferogram plane of the vibrating object are demonstrated.