Short Pulsed Laser Methods for Velocimetry and Thermometry in High Enthalpy Facilities

A suite of pulsed laser diagnostics is proposed for studying aspects of planetary entry and Earth atmospheric reentry in arc jets. For example, dissociation of molecules impacts the flow-field physics, including surface heat flux and catalytic surface reactions. Results obtained during the Phase I effort point to three promising diagnostic techniques: Rayleigh Scattering Polarimetry (RSP) for dissociation fraction, Thermal Acoustic Wave (TAW) thermometry for gas temperature, and Radar Resonance Enhanced Multi-photon Ionization (Radar REMPI) for gas temperature and velocity. The RSP technique is based on the differences in the polarization of Rayleigh-scattered light between atoms and molecules. The TAW technique is based on the determination of wave speed from the propagation of an acoustic wave generated by a laser spark from the focused beam of a pulsed laser. In the case of Radar REMPI, temperature and velocity are obtained through the spectral broadening and frequency shift associated with two-photon resonance interactions in atomic oxygen and nitrogen.