We report the results of utilization of wide-gap photorefractive sillenite crystals as adaptive photodetectors (AP) for
optical inspection of micro-electromechanical systems. The operation principle of AP is based on two-wave mixing and
non-steady-state photoelectromotive force effects in photorefractive crystals. The results of measurements of small
vibration amplitudes and resonant frequencies of the diffusely scattering objects and micro-electromechanical systems
are given. The presented adaptive interferometric systems are suitable for industrial applications.
A laser beam propagating through the atmosphere, undergoes attenuation through absorption and scattering on droplets of fog, clouds, different kinds of precipitation (rain, snow), smoke, dust; as well as it is subjected to a turbulence-induced scintillation. The resulting influence is a decrease of the information capacity of the system, rise of the bit-error rate and deterioration of the pointing accuracy at the receiver. Whereas the attenuation caused by scattering can be predicted by monitoring the weather conditions, the effects induced by turbulence have a random character and need to be overcome via some dynamic compensation procedure. This can be done using the phenomenon of wavefront reversal by means of dynamic holograms, which allows automatic compensation of disturbances. The unique advantages given by holographic technique make it rather promising to develop a relatively simple and reliable module for correction of atmospheric distortions in laser communication systems. One of the main problems though is to find an optimal medium for hologram recording that allows fast write-read-erase operation, high diffraction efficiency, high stability of characteristics and long lifetime.
An approach to compensate atmospheric disturbances in free space laser communication systems by means of dynamic holograms is considered. The possible architectures are discussed. The requirements to dynamic holographic media re specified and candidate materials are listed. Results of a modeling experiment on dynamic phase compensation in BSO crystal are presented.
The experimental investigation of the diffusion mechanism of photorefractive recording in BSO and BTO crystals at 633 nm under the conditions of sample pre-illumination by incoherent yellow-green light has been carried out. The nonmonotonic time behavior of diffraction efficiency manifesting itself as a local minimum has been found. Nothing of the kind is observed without preliminary illumination. The obtained results support the model in which the nonmonotonic evolution of a recorded grating is associated with the conditions of non-steady state and nonlinear photoconductivity in preexposed samples.