The fluorescence of atoms near a glass surface

Fluorescence spectra of atomic vapours may contain sub-Doppler structure due to the transient behaviour of the light-induced polarization of atoms which have just collided at the wall of the cell containing the vapour. This structure arises in spectra measured in reflection and in emission produced by atoms within a wavelength distance from the entrance window of the cell. Excitation spectra of transmitted light and laterally scattered light are not affected by the atom–wall collisions. Absorption and dispersion of light in an atomic vapour is conventionally described by a complex-valued and frequency-dependent index of refraction. In the presence of atom–wall collisions this theoretical description fails. This report gives an account of how the theory may be modified to include atom–wall collisions; it is assumed that the induced polarization of an atom is lost in such collisions. The modified theory qualitatively describes the experimental results. We review the conventional theory, the modified theory and the experiments featuring sub-Doppler structure related to the transient polarization behaviour.