Intracavity Raman Scattering from Molecular Beams: Direct Determination of Local Properties in an Expanding Jet Beam

An intracavity crossed laser-beam, molecular-jet-beam system has been developed for studying the properties of expanding jet beams by means of light scattering. Raman scattering has been used to measure the local rotational temperature and absolute density of monomers in a jet beam of C${\mathrm{O}}_2$ as a function of axial distance from the nozzle. A well-defined rotational temperature has been observed. This temperature drops rapidly for distances of a few nozzle diameters in agreement with isentropic theory and thereafter remains roughly constant.