Two-photon evanescent-volume wave spectroscopy: A new account of gas-soliddynamics in the boundary layer

A novel type of laser spectroscopy for the investigation of the collisional dynamics of atoms in the close vicinity of a surface has been developed. T he technique utilizes excitation of the vapor atoms in two crossed laser fi elds, one of which is directed normally to the sueface, whereas the other o ne excites an evanescent wave propagating along the surface. The results, o btained for sodium atoms near a dielectric prism surface. are quantitativel y reproduced by a rigorous theoretical approach. This new, nonintrusive met hod allows one to distinguish by purr optical means between different group s of atoms and to extract their two-dimensional velocity distributions.