SATURATION OF RESONANT WAVE MIXING IN EXCITED POUR-LEVEL MEDIA

Wave mixing in a four-level system with coherent three-frequency excit ation formed by two strong and one weak fields is considered. It was a ssumed that a strong monochromatic field at a frequency omega(e) popul ates excited electronic states, and waves with frequencies omega(1) (s trong) and omega(2) (weak) create a biharmonic perturbation in a band of fluorescent transitions of an excited system. Components of the non linear polarization p(NL) at frequencies omega(3) = 2 omega(1) - omega (2) and omega(4) = omega(e) + omega(1) - omega(2) are calculated for t he steady-state case in all orders in the field strengths of omega(e) and omega(1) and in the first order in the amplitudes of all the remai ning waves. It is shown that a feedback at the frequency omega(d) = om ega(1) - omega(2) affecting oscillating populations of levels appears in strong pumping field (omega(e)). The differences in dependences of p(NL)(omega(3)) and p(NL)(omega(4)) on the frequency detuning wd and t he intensity of external fields are determined. The possibilities for using saturation of resonant wave mixing for studying photodynamics of multilevel systems are discussed.