Abstract

The van der Waals attraction between an atom (or molecule) and a surface is ubiquitous in physics, chemistry, and biology. This long-range interaction is an essential feature of numerous cavity QED processes. In the case of an excited atom lying close to a dispersive dielectric medium, it has been predicted that the interaction can be magnified, relative to the attraction by a perfectly reflecting surface, when part of the virtual emission of the atom is coupled to the absorption spectrum of the dielectric surface,¹ As an example of such a predicted coupling, one can quote the system Cs atom (in 6D_3/2 state)/sapphire surface.² Indeed, the well-known spectrum of sapphire shows that [ε(ω) − 1]/[ε(ω) + 1) is resonant around 12.21 μm (with a slight dependence on the sapphire crystalline orientation), whereas the 6D_3/2 level can decay to a 7P_1/2 level by a transition around 12.15 μm. For the probing of such an effect, selective-reflection (SR) spectroscopy appears quite convenient it is one of the few methods enabling an excitation of the shortlived 6D_3/2 level in the vicinity of the surface. Moreover, high-resolution (FM) SR spectroscopy, which typically probes the vapor one optical wavelength away from the surface, has been repeatedly demonstrated to be a sensitive tool of the surface van der Waals interaction.³

© 1998 Optical Society of America