Abstract

Adaptive interferometer with photorefractive crystal is well known as simple and efficient instrument for measuring small vibrations and phase modulations. In most applications the fast response time of the photorefractive crystal is needed and many efforts were bent to develop the setups with the photorefractive semiconductors and sillenite crystals, which have fastest response time. However these crystals have small electro-optic coefficients, which results in weak two-beam coupling even with external field enhancement of the photorefractive effect. Thus to achieve the high light efficiency and as a result the maximum sensitivity we should choose a crystal with high reflectivity even at the expense of response time. We selected for our experiments 0°- cut BaTiO₃, which provides one of the strongest grating reflectivity without resorting to an externally applied electric field. The absence of the electric field in itself is appreciable advantage, however in this case the diffusion mechanism of the photorefractive grating recording is dominant. As a result the photorefractive grating is π/2- phase shifted with respect to the interference pattern. The signal and the reference waves are in phase in the exit of the crystal, which leads to weak quadratic detection of the signal wave phase modulation.

© 2007 IEEE