Raman scattering measurements of molecular hydrogen in a low-density, arc-heated plasma

Abstract.

Raman scattering measurements of molecular hydrogen density and temperature were made in a low-density, arc-heated plasma flow. Pulsed-laser excitation was used to improve the signal-to-noise ratio in this high-background environment. Quantum-limited detection was achieved through the use of gated photon counting and a high-power Nd:YAG laser. Radial profiles of rotational temperature and density at the exit plane were measured for five power levels. In all cases the profiles were asymmetric about the centerline. The rotational temperatures were compared with the translational temperatures of atomic hydrogen from LIF studies and found to be slightly lower. This result suggests that this flow, like the cold flow, is not in translational–rotational equilibrium.