v=2←1Absorption Spectroscopy of Vibrationally Heated NO Molecules Using Optical Pumping in a Wave Guide

A tunable 5-μm spin-flip Raman laser and a carbon monoxide laser were used in a narrow wave guide to perform multiphoton absorption spectroscopy in NO. Coherent two-photon Doppler-free absorption and stepwise multiphoton absorption were observed. From this data the $\Lambda$-doubling constants $p$ and $q$ are found to have a vibrational dependence of $\Delta p=-2.2\mathrm{}\pm 1.0$ MHz and $\Delta q=-0.12\mathrm{}\pm 0.1$ MHz. The use of a wave guide has made it possible to obtain high intensities over long interaction lengths necessary for the experiment.