Raman-Nath theory of degenerate four-wave mixing in semiconductors

A theory of degenerate four-wave mixing in the Raman-Nath approximation is developed that includes transverse effects and excitation-dependent optical material properties. A microscopic model is used for the nonlinear absorption and refractive-index changes of laser-excited semiconductors. Diffusion of the excitation density is assumed to be the dominant transverse coupling mechanism. Numerical simulations of the Raman-Nath scattering spectrum are presented for the example of room-temperature bulk GaAs using steady-state illumination. The shortcomings of the standard analysis at high excitation are demonstrated.