Propagation of circularly polarized laser pulses in the $\Lambda$-scheme of degenerated levels

The results of a theoretical study of the joint propagation of two laser pulses in a resonant medium modeled by the $\Lambda$-scheme of inhomogeneously broadened quantum transitions between degenerate energy levels are presented. It is assumed that upon entering the medium, nanosecond pulses have circular polarization and identical intensity envelopes. For the listed estimates, the $\Lambda$-scheme formed by the levels $^3$P$_0$, $^3$P$^0_1$ and $^3$P$_2$ of the $^{208}$Pb isotope were chosen. It is shown that in the medium there is a transfer of energy from a high-frequency pulse to a low-frequency one, which is accompanied by a change in the characteristics of the lower pulses. The magnitude and peculiarities of the distortions depend both on the intensity of relaxation processes in the $\Lambda$-scheme and on the directions of circular polarizations of the input fields. In the limiting case of the absence of relaxation and opposite direction polarizations of input radiation in, trains of picosecond subpulses arise in the medium at the trailing edges of both pulses, the maximum intensities of which significantly exceed the peak intensities of the corresponding input pulses. If the intensity of the relaxation processes is sufficiently high, such trains do not arise. In the case of identical directions of circular polarizations of the input radiations, regardless of the magnitude of the relaxation processes, the intensity envelopes of both pulses and their polarization characteristics in the medium experience significant changes at all stages of evolution.