Collisional angular-momentum mixing of Na Rydberg states with Xe

The collisional angular-momentum mixing of the Nand Rydberg states into states of higher angular momentum with Xe as the collisional partner has been studied in zero field and in the presence of a small electric field. The collisional l-mixing cross section in zero field has been measured for 9≤n≤23 using a vapor-cell-fluorescence method and a crossed-beam technique with a selective-field-ionization (SFI) scheme as the state detector. Using the |mₗ| selectivity of the SFI, we have also investigated the final-|mₗ|-state distribution of the collisionally populated states of $l>2$. Our measurements suggest that the collisionally populated states have predominantly low |mₗ| values (|mₗ|≤2). An application of a low electric field ({~} 50 V/cm) substantially reduces the collisional population of the low-|mₗ| states, thus reducing the total cross section as well.