Imaging fluid phenomena with atomic and molecular vapor filters
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1997 by Princeton University. We present new applications and enhancements to the spectrally Filtered Rayleigh Scattering (FRS) imaging diagnostic. Measurements have been performed in the turbulent boundary layer produced by a zero pressure gradient flat plat at Mach 8 which elucidate the effect of helium injection on large-scale turbulent structure. The technique has also been extended into the ultraviolet regime by pairing the third harmonic output of a new narrow bandwidth Titanium:Sapphire laser with atomic mercury vapor filters. Filters have been demonstrated which work in both absorption and transmission mode. Two different types of narrow band transmission filters have been fabricated and characterized, one based on resonant refluorescence, and the other based on resonance enhanced dispersion. A new pulse-burst laser, capable of outputting high power, narrow spectral bandwidth pulses at MHz rates has been paired with a framing CCD camera to obtain high-speed filtered scattering movies of turbulent Mach 2.5 flow over a 14 wedge. The images illustrate the correlation of unsteady oblique shock motion with large-scale boundary layer structure.
