A Pump-Probe Laser-Induced Fluorescence Diagnostic for Visualization and Velocimetry in High-Enthalpy Tunnels

Abstract

In this paper we present a relatively inexpensive diagnostic using atomic rubidium that can provide flow visualization and velocimetry in high-enthalpy shock tunnel flows and flames at kHz rates. A two-stage excitation scheme using 5s2 S1/2 → 5p2 P3/2 → 6d2 D3/2 of rubidium is being developed to overcome the issue of fluorescence trapping observed with single-stage excitation from and fluorescence back to the ground state. Alongside this experiment, a model of the fluorescence from both of the excited states in rubidium is being developed. This paper will discuss the diagnostic technique, the rubidium fluorescence model, the proof-of-concept measurements obtained with a rubidium vapor cell, and the current progress of the diagnostic as applied to the T-ADFA free-piston shock tunnel. Show more