Rubidium Atomic Line Filtered (RALF) Doppler Velocimetry

We report the successful proof-of-concept demonstration of the Rubidium Atomic Line Filtered (RALF) Doppler velocimetry technique. RALF is a high-velocity and high-acceleration adaptation of the Global Doppler Velocimetry (GDV) method developed in the 1990s by aerodynamics researchers [H. Komine, U.S. Patent {\#}4919536]. Laser velocimetry techniques in common use within the shock physics community ($e.g$. VISAR, Fabry-Perot, PDV) decode the Doppler shift of light reflected from a moving surface \textit{via} interference phenomena. In contrast, RALF employs a completely different physical principle: the frequency-dependent near-resonant optical transmission of a Rb/N$_{2}$ gas cell, to convert the Doppler shift of reflected $\lambda_{0} \approx $ 780.24 nm light directly into transmitted light intensity. The single-point RALF apparatus used in these experiments is fiber optic based, and incorporates a simultaneous PDV measurement channel as an ``internal standard'' for validation of the RALF results. Future plans include ``line-RALF'' experiments with streak camera detection, and two-dimensional surface velocity mapping using pulsed laser illumination and gated intensified CCD camera detection. [RW PA{\#}4931]