Influence of the absorption grating on the diffraction efficiency in thick photovoltaic media in transmission geometry under non linear regimes

With simultaneous phase and absorption gratings, we calculated the contribution of the absorption grating to the total diffraction efficiency in thick samples (≈ 1 cm) of iron doped LiNbO₃. We considered transmission geometry, with an applied field of 5 kV/cm. First we solved numerically the set of partial, non linear, material rate differential equations. These solutions were used to calculate the energy exchange in two wave mixing. We solved numerically the beam coupling equations along sample thickness, for different values of grating period. For the used value of iron doping, we found that the contribution of the absorption grating is less than 0.02% of the total value of the diffraction efficiency.