Laser Scattering Diagnostic for Shock Front Arrival and Electron Number Density

Three diagnostic methods are proposed for measuring properties of interest in the post-shock regions of a hypersonic bow shock wave that is used for studying planetary entry and earth reentry flows. Shock location is measured using an imaging approach by laser Rayleigh scattering from molecules, shock velocity is measured by beam deflection via schlieren effects, and electron number density is measured by Thomson scattering. The Rayleigh and Thomson scattering methods are complimentary to each other and can use the same pulsed laser. The schlieren deflection is accomplished with a continuous wave laser and can be used to generate a precise arrival time and provide triggering for the pulsed laser. Thomson and Rayleigh scattering imaging may be extended to MHz rates with pulse burst laser technology, providing a capability to time-resolve the motion of the shock wave as it passes through the test section. The electron density measurement is a direct technique with the potential for high accuracy time and space-resolved measurements. The Phase I effort will demonstrate all three techniques in laboratory environments at relevant conditions.