Transformation of the spectrum of an intracavity field by a resonantly absorbing medium

Analytic expressions are obtained for the spectral composition of laser radiation inside a resonator cavity filled with a gas of two-level atoms. The intracavity radiation field is approximated by a trichromatic field with an intermode frequency interval governed by the laser resonator frequency Ω = c\/2L (L is the resonator cavity length). The radiation spectrum consists of a large number of harmonics which are multiples of Ω. The amplitudes of these harmonics exhibit a periodic dependence on the concentration of the absorbing atoms and on the resonator length. The maxima of the harmonics correspond to specific relationships between the parameters, which are the conditions for what is known as an intracavity parametric resonance.