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Optical actuators based on photorefractive materials controlled by moving holographic gratings

Generating a moving holographic grating in a slab of photorefractive crystal can turn it into a smart optical material making up an optically driven actuator. Actuation occurs as a result of mechanical deformation of the crystal caused by photogenerated electric charge distribution due to piezoelectric effect. The charge distribution is periodical since it is produced by a holographic grating generated by two interfering coherent laser beams. In case of static grating with oscillating amplitude or grating vibrating near the static position the effect results in appearance of a surface acoustic wave or in bending bulk crystal as has been recently demonstrated for BSO. In this paper we focus ourselves on periodical surface deformation moving synchronously with running holographic grating. This running surface wave of deformation is similar to that being used to push a rotor pressed by its surface against a vibrating stator in so-called ultrasonic motors. It can be potentially used in optically driven actuators, which could be small in size (nanometers), less power consuming, and less affected by RF interference. We report on an appearance of a periodical surface deformation in photorefractive crystals of iron doped lithium niobate that is produced by a holographic grating. The amplitude of the deformation is of the order of 10 nm. We also report light-induced mechanical motion of micron-size particles associated with self-diffraction of weak laser beams in strongly absorbing solutions of phthalocyanines. These results might find some applications in new types of all-optical and electrooptical actuators.