Extracting parameters from slanted non-uniform gratings recorded in photopolymer

Abstract

Despite the physical significance of the slanted holographic gratings, most materials research presented in literature involves the use of the unslanted recording geometry. A physically accurate electromagnetic model of the slanted holographic non-uniform gratings recorded in photopolymers is necessary in order to extract key material parameters. In this paper we present derivation of a model based on a set of two coupled differential equations, which include the effects of: (i) An exponential decay of refractive index modulation in the direction of the beam propagation due to the variation of absorption with depth; (ii) Gaussian profile of refractive index modulation due to recording by finite Gaussian beams profile, and (iii) A quadratic variation in the spatial period of the grating (i.e. chirp). The model is applied to fit experimental data, i.e. angular scans, of unslanted gratings recorded in Polyvinylalcohol/Acrylamide material for different slant angles in order to extract key volume grating parameters.