Spectroscopy of atoms confined to the single node of a standing wave in a parallel-plate cavity

We have performed spectroscopy on sodium atoms that are optically channeled in the single node of a laser standing wave set up across a parallel-plate cavity. Using this technique we have extended our previous measurement of the Lennard-Jones van der Waals energy-level shift [Sandoghdar et al., Phys. Rev. Lett. 68, 3432 (1992)] down to a cavity width of {~}500 nm. We discuss the applications of this technique to the precise measurement of atom-surface distances. {} 1996 The American Physical Society.