Polarization spectroscopy of a velocity-selected molecular sample

This Letter demonstrates polarization spectroscopy of a velocity selected and vibrationally excited molecular sample. Specifically, the anisotropy induced by a circularly polarized IR pump beam tuned to the R(14.5)(1/2)v=1←v=0 transition of nitric oxide is observed using an IR probe resonant with the R(15.5)(1/2)v=2←v=1 hot band transition. Using two detectors in combination with the rapidly swept probe allows both the absorptive and dispersive components of the excited state polarization to be observed for the first time. The data are well described by simulations based upon a three-level density matrix model.