An approach is developed to obtain a satisfactory description of the saturation effect accompanying a resonant interaction between multifrequency radiation and an active medium. The suitability of the approach is demonstrated using examples of many-level media with parallel and cascade transitions.
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.
The example of two-frequency radiation is used in an analysis of a resonant antiparallel degenerate four-wave interaction of multifrequency radiation involving cascade transitions in diatomic molecules. The approximation of homogeneous broadening of spectral lines is used in the derivation of equations describing transient interaction of waves in fields of arbitrary intensity allowing for the diffusion of particles in a gas. Numerical calculations illustrate some characteristics of the two-frequency four-wave interaction in resonant media.