Frequency conversion to the second harmonic in different-layer nonlinear media.

The process of frequency conversion in a multilayer structure of different media with quadratic nonlinearity is investigated by using the constant-intensity approximation. The values of complex amplitudes of the fundamental radiation and the second harmonic at the outlet of each layer are the entrance values of the corresponding complex amplitudes of the next layer. Analytical expressions for second-harmonic conversion efficiency for the case of n layers are proposed. The factors restricting the efficiency of the process of frequency conversion are analyzed. In layered media, upon frequency conversion, from one layer to the next the optimum values of the phase mismatch between layers changes. The character of the process of frequency conversion of the fundamental radiation to the second harmonic depends not only on the value of the nonlinear coefficients of waves, the phase mismatch, but also on the signs of these parameters.