Preparation and detection of alignment with high Vertical BarmVertical Bar selectivity by saturated laser optical pumping in molecular beams

We describe a technique for preparation of molecules in single Vertical BarmVertical Bar 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 Vertical BarmVertical Bar 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 Vertical BarmVertical Bar-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