RESONANT 4-WAVE FREQUENCY MIXING IN DOPPLER-BROADENED TRANSITIONS

The influence of nonlinear interference processes and of changes in po pulations in strong electromagnetic fields, and also of the Doppler br oadening on resonant four-wave frequency mixing is investigated for a system-of Raman-type transitions. The case in which a quantum system i nteracts with oil weak; field and two strong fields is considered. Eac h of the energy levels is assumed to be perturbed by just one strong f ield. It is shown that the Doppler broadening alters drastically the c ontributions of the populations of the various levels to the investiga ted process and that this can alter by several orders of magnitude the nonlinear susceptibilities averaged over the velocities and influence significantly the selection of optimal configurations of the transiti ons and of the experimental conditions for effective resonant four-wav e conversion of the radiation frequencies, A numerical analysis of the derived expressions is used to account for the experimentally observe d considerable differences between the spectral dependences of the out put power and the conclusions drawn from perturbation theory.