Holographic characterization of diffraction grating modulation in photopolymers

In general, the holographic grating refractive index profiles in photopolymer materials are not identical to the exposing pattern. During exposure, high harmonics of the fundamental refractive index period are generated within the layer volume. A set of equations to calculate the amplitudes of the higher harmonics of refractive index induced in the grating is introduced. Then, an algorithm involving the use of the 3D nonlocal photopolymerization-driven diffusion model is presented and applied to calculate the resulting grating diffraction efficiencies. The experimental observation that the grating diffraction efficiency cannot reach the theoretical maximum value (eta(max) = 100%) and that, in the case of over-modulation, the minimum value (eta(min) = 0%) is also never achieved, are explained theoretically. The predictions of the simulations are also fit to experimental data for an acrylamide/polyvinyl alcohol photopolymer material with good agreement being achieved. (C) 2018 Optical Society of America