In situ characterization of an optical cavity using atomic light shift

We report the precise characterization of the optical potential obtained by injecting a distributed-feedback erbium-doped fiber laser at 1560 nm to the transverse modes of a folded optical cavity. The optical potential was mapped in situ using cold rubidium atoms, whose potential energy was spectrally resolved thanks to the strong differential light shift induced by the 1560 nm laser on the two levels of the probe transition. The optical potential obtained in the cavity is suitable for trapping rubidium atoms and eventually to achieve all-optical Bose-Einstein condensation directly in the resonator.