Elementary Sisyphus process close to a dielectric surface

We investigate both theoretically and experimentally an elementary Sisyphus process occurring during the reflection of an atom onto a laser evanescent wave propagating at the surface of a dielectric prism. Cesium atoms bouncing at normal incidence may undergo a spontaneous Raman transition between their two hyperfine levers; this leads to an efficient cooling since those levels are light shifted by a different amount by the laser-atom interaction thanks to the large hyperfine splitting. We compare the measured final energy distributions after the bounce with Monte Carlo simulations. A quantitative agreement is obtained when the van der Waals interaction between the cesium atoms and the dielectric prism is taken into account.