Volume Transmission Holograms in Lithium Niobate Crystals with Surface Copper Doping for Photovoltaic Tweezers

The results of experimental studies, theoretical analysis and numerical simulations of the features of the volume transmission holograms' formation by the interference pattern of laser beams with high contrast in the X-cut LiNbO3:Cu, fabricated by diffusion from a metal film, are presented. Analytic formulas that take the inhomogeneities of the distribution of copper ions and the absorption index of recording beams over the thickness of the sample into account are derived to describe the time evolution of the amplitude of the first spatial harmonic of the field. The material parameters of the LiNbO3:Cu structure are estimated. A comparative analysis of the spatial distribution of the amplitude of the first harmonic of the photorefractive hologram’s field in two types of LiNbO3:Cu structures is performed. We concluded that it is necessary to use X‑cut LiNbO3:Cu diffusion structures characterized by similar distributions of impurity centers, which maximums are localized near the boundary used to capture micro- and nanoparticles, for the implementation of photovoltaic tweezers.