Evanescent Waves Probe Gas-Solid Interface

A spectroscopic technique developed by a group from Odense Universitet in Denmark, Max Planck Institut für Strömungsforschung in Göttingen, Germany, and the Russian Academy of Sciences in Moscow enables the measurement of the two-dimensional velocity distribution of gas atoms at the surface of a solid. The method, which the team described in the Feb. 19 issue of Physical Review Letters, excites fluorescence in the target with an evanescent wave propagating along the surface and a volume wave normal to the surface.

The researchers used a truncated glass prism as the sample surface and tunable ring dye lasers as the excitation sources. Two-photon spectra of sodium vapor enabled them to distinguish different collisional behaviors as well as velocity distributions of the atoms normal and along the surface.