Two-photon transitions in cold caesium atoms confined in a hollow-core optical fiber*

We present the results of our experimental studies of cascade and lambda-type two-photon transitions in laser-cooled caesium atoms loaded inside a hollow-core photonic-crystal fibre. We investigate the enhancements of the two-photon processes by the tight confinement of the propagating light and from the slow-light effects arising in the optically thick atomic ensemble. We also explore the applications of these transitions for all-optical switching, cross-phase modulation, and light storage.