Abstract

The universal long-range van der Waals type atom-surface attraction was demonstrated to be susceptible of a resonant enhancement (with a possible change sign) when the virtual atomic emission can resonantly couple to a virtual absorption process in a surface mode [1]. Such an apparently exotic process, moreover limited to an (emitting) excited atom, can be in the principle generalized provided that the surface excitation originates in the continuum of a thermal excitation. For a strong temperature dependence to occur, it is needed to find a material whose surface resonances fall in the thermal infrared, and to look for an atomic level exhibiting strong dipole couplings in the same thermal IR range. This provides a key motivation to perform Selective Reflection (SR) spectroscopy, the appropriate technique to probe atom-surface interaction at a distance on the order of a (reduced) wavelength, at a fluoride window. Indeed, materials such as CaF₂, BaF₂, MgF₂, are typically transparent in the visible while exhibiting remote surface resonances [2] respectively at ~24.0 μm, 32 μm and 18.5 μm. Because the excited level Cs(8P) exhibits a strong virtual absorption to Cs(7D) (at 29, 36, 39 μm, depending on the considered fine structure), it is ultimately expected that the non-contact long-range Cs(8P) interaction with a hot fluoride surface could be severely dependent on the surface temperature, and could possibly be turned into a repulsion for a sufficient surface temperature.

© 2007 IEEE