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Broadband Spectroscopy

a graph of broadband spectroscopy from a number of materials
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The design of sensitive and species-selective laser diagnostics critically depends on extensive, precise, and accurate knowledge of the target and possible interfering species.

The Hanson Research Group combines the mature sensing technology of a Fourier transform infrared spectrometer (FTIR) with in-house designed high-temperature static cells to study the spectral signature of atoms and molecules over a wide range of wavelengths. This method provides remarkable wavelength coverage between 2–17 µm and is deployed in spectral measurements for many combustion-relevant species at temperatures up to 500°C [1].

Additionally, recent advances in laser technology have allowed the study of broadband spectroscopy to be extended to previously inaccessible temperatures (800+ K). We have used rapid-tuning, broad-scan lasers in conjunction with shock tube facilities, to acquire information of full-band (>100 cm-1, 100 times wider than conventional diode lasers) absorption within the test time of only a few milliseconds. The methodology is demonstrated in the figure with the world-first 1000 K ethylene spectra in good agreement with spectral simulations [2]; additional spectra (of >10 species) are available in the Stanford ShockGas-IR database [3].

a graph plotting wavelength and wavenumber against cross sections
Figure 1: Broadband ethylene (C2H4) absorption spectra measurements with rapid-tuning lasers at shock-heated conditions of 995 K and 2.28 atm [2]

To learn more, check out some of our publications:

[1] A. E. Klingbeil, J. B. Jeffries, and R. K. Hanson, “Temperature-dependent mid-IR absorption spectra of gaseous hydrocarbons,” Journal of Quantitative Spectroscopy and Radiative Transfer, Vol. 107 (2007), Issue 3, pp. 407–420. DOI: 10.1016/j.jqsrt.2007.03.004

[2] C.L. Strand, Y. Ding, S.E. Johnson, and R.K. Hanson, “Measurement of the mid-infrared absorption spectra of ethylene (C2H4) and other molecules at high temperatures and pressures,” Journal of Quantitative Spectroscopy and Radiative Transfer, Vol. 222–223 (2019), pp. 122–129. DOI: 10.1016/j.jqsrt.2018.10.030

[3] Y. Ding, W. -W. Su, S. E. Johnson, C. L. Strand, and R. K. Hanson, “Temperature-dependent absorption cross section measurements for propene, 1-butene, cis-/trans-2-butene, isobutene and 1,3-butadiene in the spectral region 8.4–11.7 µm,” Journal of Quantitative Spectroscopy and Radiative Transfer, Vol. 255 (2020), 107240. DOI: 10.1016/j.jqsrt.2020.107240