On the aproximate formulae and the exact method to compute wavefront reflectivity in degenerate four-wave mixing

Wavefront reflectivity in a conventional degenerate four-wave mixing (FWM) configuration can be calculated, using either approximate formulae, or exact numerical methods to solve the nonlinear coupled-wave equations. We have computed the wavefront reflectivity for FWM in a transmission and reflection geometry, respectively, using these two different methods. A comparison between them indicates that these formulae are reasonable approximations when beam coupling, diffraction efficiency and absorption are all low, and especially in the case of transmission geometry.