Welcome to the new version of CaltechAUTHORS. Login is currently restricted to library staff. If you notice any issues, please email coda@library.caltech.edu
Published July 5, 2023 | Accepted Version
Journal Article Open

Laser Absorption Sensor Targeting Potassium for Hypersonic Velocity, Temperature, and Enthalpy Measurements


A laser absorption-based sensor for hypersonic gas flows was developed, targeting the D1 spectroscopic transition of atomic potassium near 770 nm. The sensor applies rapid-scanning tunable diode laser absorption spectroscopy to measure velocity from the Doppler shift and to infer temperature from the hyperfine-split transition lineshape. This sensor measured velocities and temperatures across three distinct conditions and six shots in the Hypervelocity Expansion Tube at the California Institute of Technology. Velocity and temperature were sampled at 5  μs intervals, and temperature measurements were validated with a supplementary laser absorption-based sensor targeting carbon dioxide transitions near 4.2  μm. Measured velocities across the three conditions ranged from 3.3 to 4.4 km/s, and measured temperatures ranged from 900 to 1600 K. The combined measurements were used to infer the freestream specific total enthalpy, which ranged from 7 to 10 MJ/kg. Because atomic potassium naturally forms in the test gas of many hypersonic impulse facilities, similar sensors may be widely applicable to facility characterization.

Additional Information

© 2023 by the authors. Published by the American Institute of Aeronautics and Astronautics, Inc., with permission. This work was supported by the Office of Naval Research through award no. N00014-20-1-2322 with Eric Marineau as the contract monitor and by the U.S. Air Force Office of Scientific Research through award no. FA9550-19-1-0219 with Sarah Popkin as the contract monitor. Tal Schwartz acknowledges support from the NASA Space Technology Graduate Research Opportunities Fellowship. The authors would like to thank Alexander Acosta, Noel Esparza-Duran, and Michael Stramenga for assisting with operation of the Hypervelocity Expansion Tube.

Attached Files

Accepted Version - 1.j062620.pdf


Files (3.2 MB)
Name Size Download all
3.2 MB Preview Download

Additional details

August 22, 2023
October 20, 2023