Two-photon Doppler-free spectroscopy of trapped atoms

We describe the systematics of two-photon Doppler-free excitation of atoms confined in a cylindrical harmonic trap, at densities far from the regime o f quantum degeneracy. The line shape is explained in terms of momentum tran sfer between the light beam and the trapped atoms. This formalism extends t he semiclassical analysis of time-of-flight broadening. The results, which are general, were motivated by the development of two-photon Doppler-free s pectroscopy of trapped atomic hydrogen. [S1050-2947(99)04406-6].