Photovoltaic and diffusion effects in formation of 1D and 2D gratings by Bessel beam technique in LiNbO3:Fe crystal

Abstract

The study of the contributions of photovoltaic and diffusion effects in the formation of 1D and 2D holographic gratings by Bessel beam technique in photorefractive Fe doped lithium niobate crystals are performed. For this purpose 1D and 2D gratings were recorded by travelling Bessel beam and counter-propagating Bessel beam (CPBB) techniques using laser radiation at 532nm wavelength and 17 mW power. Created 1D grating in the form of concentric rings had 9.0μm period in radial direction. 2D grating which is a combination of annular and planar gratings had a period of 9.0μm in radial and 266 nm in axial directions. The testing of the profile of the recorded gratings by phase microscope was performed. The investigations show that the refractive index depth of modulation for 1D annular grating has pronounced azimuthal dependence as a result of formation of gratings predominantly by the photovoltaic effect taking place along the C-axis of the crystal. For 2D grating formed by CPBB technique the azimuthal dependence of grating modulation depth is less pronounced. The 266 nm period in axial direction provides, except for the photovoltaic effect, also the contribution of the diffusion of charge carriers to the grating formation. Diffusion effect takes place in all directions and provides the isotropic contribution to the grating formation, but with less efficiency than the photovoltaic effect.