Calculation of the influence of the absorption grating on the diffraction efficiency in photovoltaic media in reflection geometry for nonlinear regimes

With simultaneous phase and absorption gratings, we calculated the contribution of the absorption grating to the total diffraction efficiency in thick samples (around 0.5 cm) of iron doped lithium niobate with an applied electric field between 0 and -400 kV/cm in reflection geometry. We started by solving numerically the set of partial, non-linear, material rate differential equations. Then, we used these solutions to find numerical solutions in a self-consistent way to the beam coupling equations in two-wave mixing along sample thickness. For the given set of values of physical parameters of lithium niobate, we found that the presence of the absorption grating has a weak influence on the diffraction efficiency. It diminishes the total value of the diffraction efficiency in a small amount of around only 1%.