Three-dimensional spatial diffusion in optical molasses

Abstract

We have studied the expansion of a small cloud of85Rb atoms in three-dimensional optical molasses (lin ⊥ lin and σ+ − σ− configurations) and observed diffusive motion. We determined the spatial-diffusion coefficients for various laser intensities and detunings, and compared them (in the case of lin ⊥ lin molasses) to values calculated from friction and momentum-diffusion coefficients of a one-dimensional (1D) theory of laser cooling. The predicted variations of the spatial-diffusion coefficient with laser intensity and detuning are in good qualitative agreement with the experimental data. We found that the minimal value observed experimentally, ≈ 6 × 10−4 cm2/s, lies within a factor of 3 of the 1D theoretical minimum, ≈, 26ħ/M, whereM is the atomic mass.