Coherent anti-Stokes Raman scattering is applied to the study of rovibrational populations in magnetic multicusp H2 and D2 discharges. This subject is of interest to negative hydrogen ion formation by volume plasma processes. The populations of high-lying rotational states (J≳5) in the vibrational levels v=0, 1, and 2 are found to be significantly higher than expected from the Boltzmann law. In H2 the net populations of the first four vibrational levels follow approximately the Boltzmann law, with the vibrational temperature of 2390 K (in a 90 V-10 A discharge at 55 μbar). In similar discharge conditions, the population of the state v=3 in D2 is higher than expected from the Boltzmann law. In the presence of the discharge a deficiency in H2 and D2 molecule density was observed and was attributed to the possible presence of H and D atoms. This was verified by an independent measurement of the atomic fraction and temperature. The density of negative ions, measured by the photodetachment technique, is also reported.

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A novel and very sensitive method for gas concentration measurements is proposed. Intense light scattering is obtained through a stimulated interaction. The method appears more practical than spontaneous Raman scattering for gas flow analysis with fine spatial resolution. Experimental results with the detection of H2 are given.

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We examine the effect of electronic resonance enhancement on the line broadening for Coherent Anti-Stokes Raman Scattering (CARS) and related third-order non linear processes, in low pressure gases. These phenomena are analysed theoretically within the framework of a time-ordered diagrammatic representation of nonlinear polarizations. Diagrams facilitate the classification of the various physical processes and provide a way to readily derive all the susceptibility contributions. In CARS, the susceptibility terms which are Doppler-free and thus prevail in the Doppler limit are different from those which dominate in the collision broadening regime. This causes important changes in the spectral content. On the contrary, the same terms are seen to dominate, in both regimes, in coherent Stokes Raman scattering or in stimulated Raman scattering. Typical line contours are displayed. The generalization to all nonlinear processes is outlined