Stanford
Hanson Research Group

Lineshape Studies

a chart showing two peaks among a range of data

Many gas diagnostic techniques rely on laser absorption spectroscopy to measure gases at extreme pressures, temperatures, and concentrations.

However, these techniques are only as accurate as parameters used to model each absorption line, which specifies the spectral lineshape.

The facilities of the Hanson Research Group can verify these lineshape parameters over a wide range of experimental conditions, extending absorption models to much higher temperatures and pressures than previously studied. One recent example is the absorption of nitric oxide (NO), which was previously only studied at temperatures up to 300 K and pressures up to about 1 atm. Through careful measurements of individual lineshapes at high temperatures and blended absorption features at high pressures, Hanson Group researchers have extended NO absorption models to 2500 K and 34 atm. These extended models are regularly deployed by our researchers and others around the world for gas sensing in hypersonic facilities and shock tunnels.

a graph plotting wavenumber against residual and absorbance
Experimental NO absorption measurements at high pressures reveal deviations from the standard Voigt absorbance model due to the ‘line mixing’ effect. The revised Stanford line mixing model matches experimental data to within 2%. [1].

To learn more, check out some of our publications:

[1] W.-W. Su, C. Boulet, C. A. Almodovar, Y. Ding, C. L. Strand, and R. K. Hanson, “Line Mixing Study on the Fundamental Rovibrational Band of Nitric Oxide near 5.3 μm,” Journal of Quantitative Spectroscopy and Radiative Transfer, submitted 2021

[2] C. A. Almodovar, W.-W. Su, R. Choudhary, J. K. Shao, C. L. Strand, and R. K. Hanson, “Line mixing in the nitric oxide R-branch near 5.2 μm at high pressures and temperatures: measurements and empirical modeling using energy gap fitting,” Journal of Quantitative Spectroscopy and Radiative Transfer, Vol 276 (2021) 107935. DOI: 10.1016/j.jqsrt.2021.107935

[3] C. A. Almodovar, W.-W. Su, C. L. Strand, and R. K. Hanson, “R-branch line intensities and temperature-dependent line broadening and shift coefficients of the nitric oxide fundamental rovibrational band,” Journal of Quantitative Spectroscopy and Radiative Transfer, Vol. 239 (2019). DOI: 10.1016/j.jqsrt.2019.106612