Sodium vapor seeded into a hypersonic helium flow through an orifice on a model is used as a tracer to determine velocity profiles. A narrow-linewidth tunable dye laser is scanned across the Doppler-shifted absorption line of the sodium and the resonant fluorescence is observed. Curves showing the velocity-shifted pressure- and temperature-broadened absorption lines at several points in the flow are presented. Fluorescence is strong enough to use this technique for quantitative flow visualization: at each laser frequency, a specific velocity component is highlighted and easily observed by eye.
