New holographic method for formation of 2D gratings in photorefractive materials by Bessel standing wave

Abstract

A counter-propagating Bessel beam technique is suggested and realized for creation of 2-dimensional (2D) holographic periodic structures (PS) in photorefractive materials. 2D PS formed by the suggested method is a combination of annular and planar gratings. The Bessel beam is formed by optical element - axicon. The recording of the gratings are performed by single mode He-Ne laser beam at 633 nm. The counter-propagating beam geometry builds up the Bessel standing wave with periodic annular structure in each anti-node. The refractive gratings are recorded in Z and Y-cut 2 mm thick Fe doped lithium niobate crystals via electro-optic effect. The read-out of 2D PS is performed by Gaussian and Bessel beams. Diffraction patterns in transmission and reflection are observed. The formed 2D PS have the halfwavelength standing wave period of ~300 nm in longitudinal direction, the period of ~10 μm in radial direction, and up to 10 % diffraction efficiency.