Light-pressure-induced line-shape of the saturation resonance dip in an atomic gas

The effect of a force of resonance light pressure on the amplitude and frequency properties of the absorption resonance dip occurring in optical saturation spectroscopy of a gas of two level atoms was studied. On the basis of numerical solutions of the Liouville and Fokker–Planck equations the behaviour pattern of the velocity distribution function of a two level atomic gas in relation to the saturation intensity and time of their interaction with a strong resonant light field was evaluated. The shape of a resonance line, related to saturated absorption, and its location relative to the frequency of the atomic transition were determined taking into account the dynamics of the velocity distribution function. It is established, that the line shape is determined by the interaction of the strong light field with slow moving atoms. The represented numerical results explained qualitatively a number of experimental facts, that could not be explained before.