Coherent anti-Stokes Raman scattering is demonstrated as a quantitative diagnostic in low-density flows by mapping H(2) velocity and translational temperature inside and outside the nozzle of a resistojet. A spatial resolution of better than 35 mum along the flow direction and 350 mum transverse to it was attained in a density as low as 5 x 10(15) cm(-3). The accuracy of the velocity, inferred from the Doppler shift of the Q (1) Raman resonance, was limited by the scan linearity of the laser to +/-0.2 km/s. Translational temperatures, inferred from linewidths and complicated by saturation and ac Stark effects, had an accuracy of ~20%. A discussion of applicability to molecular nitrogen is presented.

Coherent anti-Stokes Raman scattering velocity and translational temperature measurements in resistojets

A method for measuring the axial and transverse plume velocities and internal energy distributions in rarified thruster plumes by using pulsed laser-induced fluorescence (LIF) of atomic hydrogen Balmer lines is described. The results of an application of this technique for velocity mapping of a 30-kW ammonia arc-jet plume generated in the JPL arc-jet testing facility (which is uniquely suited for these measurements due to the end-on optical access provided by its ninety-degree-bent diffuser) are described. A schematic diagram of the JPL facility with LIF setup is included.

Daniel D. Erwin

Papers

Velocity mapping in a 30-kW arcjet plume using laser-induced fluorescence