Four-wave interaction of middle-infrared radiation in media with a thermal nonlinearity

Theoretical and experimental investigations were made of a four-wave interaction of middle-infrared radiation based on a thermal nonlinearity of absorbing liquids and gases. A study was made of the influence of parasitic effects associated with heating of a nonlinear medium (such as the thermal lens effect, frequency sweeping of interacting waves, thermal expansion of the medium, and convection) on the efficiency of the four-wave interaction and the quality of phase conjugation utilizing this interaction. The conditions under which this influence is minimal were identified. An experimental study was made of phase conjugation of CO₂ laser radiation by a four-wave interaction in CCl₄ with a high reflection coefficient (up to 20% in the cw regime). The attained phase conjugation was limited the thermal lens effect, but this could be compensated.