Anomalous components of the scattering under the conditions of a developed instability of laser radiation in a resonant medium

Experimental and theoretical investigations were made of the characteristics of an 'anomalous' component of the scattering of high-intensity laser radiation in a resonant medium (sodium vapour) observed earlier in the frequency range ω_L > ω_D2. The appearance of this component had been attributed by other authors to parametric downconversion. Contrary to this interpretation, the component in question was observed also at frequencies of ω_L < ω_D1. An analysis showed that the generation of this component and its properties can be explained fully by a four-wave interaction in a gas of three-level atoms.