Advanced Laser Spectroscopy

Classical laser absorption systems, which typically involve a diode laser scanned over a molecular transition, are often limited in their temperature range and ability to probe molecules such as homonuclear diatomics.

In the Hanson Research Group, we utilize several advanced laser techniques, such as cavity enhanced absorption spectroscopy (CEAS), two-color ultraviolet (UV) absorption spectroscopy, intensity modulation spectroscopy (IMS), and wavelength modulation spectroscopy (WMS). Each methodology has its own advantage, such as improving signal-to-noise (SNR) ratios in harsh environments, tracking species undetectable by other methods, or extending the temperature range over which high-fidelity measurements can be made.

By implementing these techniques, our group has succeeded in making highly quantitative measurements in extreme environments such as propulsion systems, hypersonic air flows, combustion engines, and industrial processes with temperatures at times exceeding 10,000 K and 100 atm.

The Hanson Research Group continues to develop new advanced laser spectroscopy to study next-generation energy and propulsion systems, as well as to gain fundamental insights into high-temperature and high-pressure gas phenomena.

graph showing number density over time — Number density time histories for the total amount of O2 (nO2) and for specific vibrational levels (nv'') measured in shock-heated 50% O2 in Argon experiments at an initial post-shock temperature of 11,410 K and 30 Torr using two-color UV absorption spectroscopy [3]. The strong UV absorption spectrum of O2 (Schumann-Runge system) allows ultraviolet lasers to probe specific vibrational quantum states in the evolution of non-equilibrium chemistry at extreme temperatures.

To learn more, check out some of our publications:

[1] W. Y. Peng, S. J. Cassady, C. L. Strand, C. S. Goldenstein, R. M. Spearrin, C. M. Brophy, J. B. Jeffries, and R. K. Hanson, “Single-ended mid-infrared laser-absorption sensor for time-resolved measurements of water concentration and temperature within the annulus of a rotating detonation engine,” Proceedings of the Combustion Institute, Vol. 37 (2019) pp. 1435–1443. DOI: 10.1016/j.proci.2018.05.021

[2] S. Wang, K. Sun, D. F. Davidson, J. B. Jeffries, and R. K. Hanson, “Cavity-enhanced absorption spectroscopy with a ps-pulsed UV laser for sensitive, high-speed measurements in a shock tube,” Opt. Express, Vol. 24 (2016) pp. 308–318. DOI: 10.1364/OE.24.000308

[3] J. W. Streicher, A. Krish, and R. K. Hanson, “Coupled vibration-dissociation time-histories and rate measurements in shock-heated, nondilute O2 and O2-Ar mixtures from 6000 to 14000 K,” Physics of Fluids, Vol. 33 (2021) DOI: 10.1063/5.0048059

[4] A. Krish, J. W. Streicher, and R. K. Hanson, “Spectrally-resolved absorption cross-section measurements of shock-heated O2 for the development of a vibrational temperature diagnostic,” Journal of Quantitative Spectroscopy and Radiative Transfer, Vol. 270 (2021) DOI: 10.1016/j.jqsrt.2021.107704