New feature in selective reflection with a highly parallel window: phase-tunable homodyne detection of the radiated atomic field

Selective reflection (SR) of light from a cesium vapor-sapphire interface close to the D-2 resonance line has been studied by use of a sapphire window with highly parallel surfaces. Temperature-tuning of the Fabry-Perot behaviour of the window [Jahier et al. , Appl. Phys. B 71, 561 (2000)], resulting in a change of 0.5 to 26% of the window reflection coefficient, dramatically affects both the magnitude and lineshape of the SR resonant atomic signal. For nearly zero window reflection, the case of particular interest, the absorptive properties of the atomic medium govern the signal shape, as opposed to the usual dispersive ones in the ördinary\" SR. This is a manifestation of homodyne detection of the radiated atomic field. The numerical simulation based on a model, which accounts for all the processes involved, shows a good agreement with the experimental spectra. Possible applications for laser and atomic spectroscopy, in particular tunable locking of laser frequency, are discussed.