Abstract

An attractive candidate for performing atom guidance is the evanescent field at the border of a dielectric light guide since providing a short range (repulsive) potential. In contrast to passive hollow capillaries, we have realised a lasing one made up from highly doped phosphate glass. Compared to its passive counterpart, the laser capillary has the big advantage that the in-coupled light being spectrally removed from the atomic transition of the atoms to be manipulated is used for pumping the laser. The capillary had a diameter of 70 μm possessing a protection coating. The bore diameter was 11 pm. The doping concentration amounted to 2·10²⁰ cm^-3 Nd³⁺. The capillary length was 1.6 cm (7 cm), butt coupled mirrors form the resonator. The capillary could be illuminated side-on or end-on with pump radiation for the active ions delivered by a diode laser at λ=805 nm. The output mirror had a transmission of < 1% to realise a high intracavity power being desirable to create a strong optical potential necessary in evanescent waveguiding of atoms. The near field distribution is shown in Fig.1. To proof the reaction of the evanescent field on an absorptive disturbance we have filled the capillary with an ir-dye (concentration ~0.07 g/1) finding a strongly modulated (mode locked) output when pulsing the diode laser, Fig.2. (The transverse damping distance in the dye solution is only ~0.3 μm). For an empty capillary the emission gets stationary after some typical relaxation oscillations. To estimate the optical potential we have made a numerical analysis of the laser field distribution in the hollow waveguide. Fig.3 shows the mode field at λ=780 nm in the capillary. We have calculated the optical potential U(r) to guide ⁸⁵Rb atoms with an intra fiber power of 2 W. The frequency detuning from the atomic resonance is 10 GHz, the saturation intensity of the atomic transition is 1.8 mW/cm The optical barrier as a function of distance from the inner surface in terms of temperature is shown in Fig.1c (inset). The realisation of active atomic waveguides may stimulate interesting studies in atom optics, near field optics and cavity QED.

© 1998 IEEE