We report on detailed studies of the effect of resonant light pressure on the optical response of an atomic gas to a single monochromatic laser field. In this very elementary situation of laser spectroscopy, the redistribution of atomic velocities that is induced by spontaneous light pressure leads to a novel contribution to the optical dispersion curve of the medium. This light-pressure-induced dispersion phenomenon displays a pronounced nonlinear dependence on the laser intensity. Moreover, for a given intensity, its strength is closely related to the laser beam diameter. As most important feature, this light-pressure-induced dispersion displays an even symmetry with respect to the optical detuning from line center. As a result, the total Doppler-broadened dispersion curve of the gas can become asymmetric, and a significant shift of the dispersion line center can occur. In addition to a detailed theoretical description of the phenomenon, we report on its experimental investigation on the \ensuremath{\lambda}=555.6 nm
1S0${\mathrm{\ensuremath{-}}}^{3}$
P1 transition in atomic ytterbium vapor with the use of frequency-modulation spectroscopy. The experimental findings are in good quantitative agreement with theoretical predictions.
We study the effect of resonant light pressure on the optical response of a Doppler-broadened atomic medium to a single monochromatic laser field. As a main consequence of the spontaneous scattering force, a novel contribution to the optical dispersion of the atomic gas is predicted, which shows a pronounced nonlinear intensity dependence; moreover, for a given laser intensity, its strength is closely related to the laser-beam diameter. Most importantly, this light-pressure-induced dispersion displays an even symmetry with respect to the optical Doppler detuning; as a result, the total dispersion curve of the medium can be changed substantially. In addition to a detailed theoretical description of the phenomenon, we propose a simple experiment based on frequency-modulation spectroscopy for the measurement of the predicted nonlinear dispersion feature.
We report the results of studying the effect of the resonant light pressure force on the amplitude and frequency properties of the nonlinear susceptibility and well known absorption resonance dip occurring in optical saturation spectroscopy of two level atomic gas. On the basis of numerical solutions of the Liouville and Fokker-Plank equations the behaviour pattern of the velocity distribution function of a two-level atomic gas in relation to the saturation intensity and time of interaction with a strong resonant optical field was obtained. Time course of the velocity distribution function due to the action of spontaneous light pressure force leads to modification of the nonlinear susceptibility, absorption saturation resonant line form and to change of frequency dip relative to the atomic resonant frequency transition. The represented numerical modeling results explained qualitatively a number ofexperimental facts, that could not be explained before.