Simultaneous forward–backward Raman scattering studies of D2 broadened by D2, He, and Ar

Abstract

Unavoidable beam crossings within a spherical-mirror, multipass stimulated Raman gain cell give rise simultaneously to forward- and backward-scattering Raman signals. In the Doppler-broadened/Dicke-narrowed regime of density, the lineshape is a function of the momentum transfer in the scattering process and thus the observed spectra will have more complex lineshapes than those seen with simple forward or backward scattering geometries. The analyses necessary to quantitatively account for such forward–backward spectra are summarized. These spectra enable unique experimental tests of the lineshape functions used for the description of the Raman Q-branch spectrum under conditions where Doppler contributions and Dicke narrowing are significant. Results for the D2:D2 and D2:He systems support the well-known Galatry, or soft collision, lineshape function. However, in the case of D2:Ar, our results suggest the need to employ the more general, complex soft collision function. In addition, these studies have provided data on linear-with-density line broadening coefficients (previously published) and line shifting coefficients (reported here) for these molecular systems.