Theory of two-wave (interference) interaction of multifrequency radiation due to cascade transitions in many-level resonant media

A theory is developed of interference interaction of multifrequency counterpropagating laser waves in many-level resonant media. Closed equations are derived for a degenerate two-wave interaction of multifrequency radiation due to cascade transitions in many-level absorbing and amplifying media in the steady-state case with strongly separated frequencies and neglecting molecular diffusion. Three-frequency radiation is used as an example in a comparison with the results obtained neglecting interference of counterpropagating waves.