Dual-comb spectroscopy for high-temperature reaction kinetics

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-C3H4/18% 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, f(r), of 9.86 GHz and a difference in comb spacing, Delta f(r), of 5 MHz, enabled a theoretical time resolution of 0.2 mu s but the data was time-integrated to 4 mu s 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.