l-state selective field ionization of rubidium Rydberg states

State-selective field ionization is widely used for the state-selective detection of Rydberg states. We demonstrate a refinement of this technique which improves the selectivity and extends its use to l-states in heavy alkalis by employing shaped field ramps. We show the increased selectivity of field ionization by a fast step followed by a slow ramp in rubidium and apply this scheme to an electron scattering experiment, corroborating dipole selection rules in fast electron scattering induced excitation