The parametric gain is computed for the case of a cubic crystal having a single lattice resonance as the frequency of one of the generated waves, the idler, is swept through the lattice resonance. It is found that as resonance is approached, the nonlinear susceptibility and the infrared absorption at the idler frequency both become resonantly large in just such a manner as to leave the parametric gain unaltered. A simple expression is derived for the parametric gain both by solving the coupled-wave equations and by calculating the transition rate for light scattering. The parametric gain is estimated numerically for gallium phosphide.

• Received 22 March 1968

DOI:https://doi.org/10.1103/PhysRev.171.1058