Abstract

A multi-MHz laser absorption sensor at 777.2 nm (${12},\!{863}\;{{\rm cm}^{- 1}}$) is developed for simultaneous sensing of (1) ${\rm O}{(^5}{{\rm S}^0})$ number density, (2) electron number density, and (3) translational temperature at conditions relevant to high-speed entry conditions and molecular dissociation. This sensor leverages a bias tee circuit with a distributed feedback diode laser and an optimization of the laser current modulation waveform to enable temporal resolution of sub-microsecond kinetics at electronvolt temperatures. In shock-heated ${{\rm O}_2}$, the precision of the temperature measurement is tested at 5 MHz and is found to be within ${\pm}{5}\%$ from 6000 to 12,000 K at pressures from 0.1 to 1 atm. The present sensor is also demonstrated in a CO:Ar mixture, in parallel with a diagnostic for CO rovibrational temperature, providing an additional validation across 7500–9700 K during molecular dissociation. A demonstration of the electron number density measurement near 11,000 K is performed and compared to a simplified model of ionization. Finally, as an illustration of the utility of this high-speed diagnostic, the measurement of the heavy particle excitation rate of ${\rm O}{(^5}{{\rm S}^0})$ is extended beyond the temperatures available in the literature and is found to be well represented by $k{(^3}P{\to ^5}{S^0}) = 2.7 \times {10^{- 14}}{T^{0.5}}\exp (- 1.428 \times {10^4}/T)\;{{\rm cm}^3} \cdot \;{{\rm s}^{- 1}}$ from 5400 to 12,200 K.

© 2023 Optica Publishing Group

Shock-tube measurements of excited oxygen atoms using cavity-enhanced absorption spectroscopy

Marcel Nations, Shengkai Wang, Christopher S. Goldenstein, Kai Sun, David F. Davidson, Jay B. Jeffries, and Ronald K. Hanson
Appl. Opt. 54(29) 8766-8775 (2015)

Near-MHz temperature and H₂O measurements in post-detonation fireballs of 25 g hemispherical explosives using scanned-wavelength-modulation spectroscopy

Charles J. Schwartz, Joshua W. Stiborek, Austin Butler, Damon Chen, Daniel R. Guildenbecher, Marc Welliver, Nick Glumac, and Christopher S. Goldenstein
Appl. Opt. 62(6) 1598-1609 (2023)

Quantum-cascade-laser-absorption-spectroscopy diagnostic for temperature, pressure, and NO X ² Π _1/2 at 500 kHz in shock-heated air at elevated pressures

Jonathan J. Gilvey, Morgan D. Ruesch, Kyle A. Daniel, Charley R. Downing, Kyle P. Lynch, Justin L. Wagner, and Christopher S. Goldenstein
Appl. Opt. 62(6) A12-A24 (2023)

Four-color fiber-coupled mid-infrared laser-absorption sensor for temperature, CO, CO₂, and NO at 5 kHz in internal combustion engine vehicle exhaust

Joshua W. Stiborek, Charles J. Schwartz, Nathan J. Kempema, Joseph J. Szente, Michael J. Loos, and Christopher S. Goldenstein
Appl. Opt. 62(32) 8517-8528 (2023)

Stark broadening of the cesium 5²D_5/2 → 10²F line shape

Timothy M. True, Christopher A. Rice, Greg A. Pitz, and Glen P. Perram
J. Opt. Soc. Am. B 40(12) 3015-3021 (2023)