Dual-comb spectroscopy for high-temperature reaction kinetics
Nicolas Hunter Pinkowski, Yiming Ding, Christopher L Strand, Ronald K Hanson, Raphael Horvath, Markus Geiser
Abstract
Abstract In the current study, a quantum-cascade-laser-based dual-comb spectrometer (DCS) was used to paint a detailed picture of a 1.0 ms high-temperature reaction between propyne and oxygen. The DCS interfaced with a shock tube to provide pre-ignition conditions of 1225 K, 2.8 atm, and 2% p-C 3 H 4 /18% O 2 /Ar. The spectrometer consisted of two free-running, non-stabilized frequency combs each emitting at 179 wavelengths between 1174 and 1233 cm −1 . A free spectral range, <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msub> <mml:mi>f</mml:mi> <mml:mi>r</mml:mi> </mml:msub> </mml:mrow> </mml:math> , of 9.86 GHz and a difference in comb spacing, <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mi mathvariant="normal">Δ</mml:mi> </mml:mrow> <mml:mrow> <mml:msub> <mml:mi>f</mml:mi> <mml:mi>r</mml:mi> </mml:msub> </mml:mrow> </mml:math> , of 5 MHz, enabled a theoretical time resolution of 0.2 µs but the data was time-integrated to 4 µs to improve SNR. The accuracy of the spectrometer was monitored using a suite of independent laser diagnostics and good agreement observed. Key challenges remain in the fitting of available high-temperature spectroscopic models to the observed spectra of a post-ignition environment.