Cousens, SamuelO’byrne, Sean2026-07-032026-07-039781624106354ORCID:/0009-0007-2076-6766/work/219175483https://hdl.handle.net/1885/733812302In 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.The authors would like to acknowledge support from the US Air Force Asian Office of Aerospace Research and Development, through Grant FA2386-19-1-4023. The authors would also like to thank Graeme Poleweski for operating the T-ADFA hypersonic wind tunnel.enPublisher Copyright: © 2022, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.202210.2514/6.2022-364085135067222