1- and 2-photon absorption by laser-cooled ⁸⁵Rb using an optical nanofiber

The characteristics of a cold cloud of ⁸⁵Rb can be non-destructively examined using an optical nanofiber. The nanofiber is a submicron-diameter cylindrical waveguide fabricated from commercially-available optical fiber using a heat-and-pull rig. The nanofiber can be used as a 'dark' or 'bright' probe depending on whether laser light is coupled into the nanofiber. We demonstrate the use of an optical nanofiber as an absorption spectroscopy tool for cold atoms. A frequency-scanned probe beam is launched through the nanofiber and the resonant light is absorbed at the waist of the nanofiber by nearby cold ⁸⁵Rb atoms. We present recent singlephoton absorption results and comment on the role of surface interactions. Future work on 2-photon absorption using excited state electronic transitions in ⁸⁵Rb is discussed.