Preparation and detection of alignment with high ‖m‖ selectivity by saturated laser optical pumping in molecular beams

Abstract

We describe a technique for preparation of molecules in single ‖m‖ levels involving saturated laser optical pumping on molecular P, R, and Q transitions. This technique is not limited to small rotational quantum numbers j. It allows the determination of the populations of ‖m‖ levels for arbitrary distribution functions f ( j,m) or alternatively, the determination of all moments of f ( j,m). In principle, this method is able to completely determine the angular distribution of j vectors. Experimental verification of the high ‖m‖-state purity achieved in Na2 supersonic beams, as well as of inherent limitations due to hyperfine interaction is provided. For illustration, experimental data on laser-induced alignment, the dependence of the flow induced molecular alignment, and on Δm-propensity rules in differential rotationally inelastic scattering are presented.