Observation of Light-Pressure-Induced Line-Shape Asymmetries of Saturated Absorption and Dispersion Resonances

Abstract

This chapter presents a simple qualitative explanation of the light-pressure-induced line-shape asymmetries in saturation spectroscopy. This method is based on the velocity-selective excitation of a certain velocity subgroup in a gas by a relatively strong optical pump field. The induced hole occurring at the resonant velocity in the population difference of ground and excited state, which is known as Bennett hole, is probed by a weak tunable test field. As a consequence, Doppler-free signals occur in both the absorption and the dispersion curve of the test field. Usually, these Doppler-free signals are considered as being completely attributed to a perturbation of the internal atomic degrees of freedom, namely, the saturation of the optical transition. However, the external atomic degrees of freedom can also experience a perturbation—the redistribution of atomic velocities caused by the spontaneous light pressure of the saturating field. The chapter presents experiments that demonstrate that resonant light pressure can lead to substantial modifications of the line shapes of Doppler-free absorption and dispersion resonances obtained by saturation spectroscopy in low-pressure gases.