<title>Optical actuators based on photorefractive materials controlled by holographic gratings</title>

Abstract

All-optical actuators based on static or moving holographic gratings could have an advantage over current actuators because of their smaller size, less power and less RF interference. Instead of an ultrasonic wave produced by an electrically driven piezoelectric actuator as in ultrasonic motors, the wave resulted from mechanical deformation of the crystal caused by photo-generated electric charge distribution due to the converse piezoelectric effect. The charge distribution was periodical since it was produced by a holographic grating generated by two interfering coherent laser beams. Surface gratings associated with holographic volume gratings in photorefractive crystals of iron-doped lithium niobate have been studied using diffraction of a reflected probe beam and high-resolution phase-shifted interferometric profilometry. Both techniques show that the surface gratings do in fact exist in the form of periodical corrugations of the same period as that of the volume grating. The maximum amplitude of the surface grating measured by both techniques was close to 6.5 nm. We also demonstrated that the periodical electric forces on the surface were capable of assembling polystyrene microspheres along the fringes of the grating.