Analytical solution of the non-monochromatic directed radiation transfer in a resonantly absorbing medium

In this work, a stationary problem analytical solution of the non-monochromatic directional radiation transfer through a medium filled with alkali metal atoms and a buffer gas is obtained. The three-level atom approximation was used to describe the level population kinetics. The processes of absorption and stimulated emission of photons, collisional mixing of the levels of the alkali metal atom fine structure, and spontaneous transitions were taken into account. The absorption of spontaneous radiation by the medium was not taken into account. Using the example of a medium consisting of potassium vapor and a helium buffer gas, the analytical and numerical solutions are compared.