Fully resonant four-wave mixing in optically thick Doppler broadened medium

Summary form only given. Coherent coupling processes in multilevel schemes have recently gained tremendous attention in connection with attempts to manipulate nonlinear-optical response, level populations, and refraction indices of the resonant medium. While single and multiphoton resonances are approached, giant enhancement of nonlinear-optical cross-sections occurs. At the same time, many other accompanying effects raise and interplay.