Coherent Scattering of Light by Bose--Einstein Condensation in a Tight Confinement

We have observed strong scattering of probe light by dilute Bose--Einstein condensate (BEC) ⁸⁷Rb gas in a tight magnetic trap. The scattering light forms fringes at the image plane. It is found that we can infer the real size of the
condensation and the number of the atoms by modelling the imaging system. We present a quantitative calculation of light scattering by the condensed atoms. The calculation shows that the experimental results agree well with the prediction of the generalized diffraction theory, and thus we can directly observe the phase transition of BEC in a tight trap.