QCL-Based Dual-Comb Spectrometer for Multi-Species Measurements at High Temperatures and High Pressures

Abstract

Rapid multi-species sensing is an overarching goal in time-resolved studies of chemical kinetics. Most current laser sources cannot achieve this goal due to their narrow spectral coverage and/or slow wavelength scanning. In this work, a novel mid-IR dual-comb spectrometer is utilized for chemical kinetic investigations. The spectrometer is based on two quantum cascade laser frequency combs and provides rapid (4 µs) measurements over a wide spectral range (~1175–1235 cm−1). Here, the spectrometer was applied to make time-resolved absorption measurements of methane, acetone, propene, and propyne at high temperatures (>1000 K) and high pressures (>5 bar) in a shock tube. Such a spectrometer will be of high value in chemical kinetic studies of future fuels.

Monitoring formaldehyde in a shock tube with a fast dual-comb spectrometer operating in the spectral range of 1740–1790 cm–1

“…Fig. 5) for the purpose of extracting timedependent concentration profiles [40], even if the linewidth of individual absorption lines of the species may be smaller than the spectral point spacing of the comb teeth (undersampling), as is the case in the current work. Newbury et al [41] define a figure of merit for dual-comb spectroscopy systems as the product of the SNR (the root-mean-square absorption noise level) normalized by the square root of the acquisition time, and the number of resolved spectral elements.…”

A methane line list with sub-MHz accuracy in the 1250 to 1380 cm−1 range from optical frequency comb Fourier transform spectroscopy

“…The results were in good agreement with the earlier study by AlSaif et al [42,43], who recorded the ν1 fundamental band using a comb-referenced continuous-wave (CW) quantum cascade laser. While dual-comb spectroscopy with quantum-cascade lasers has been successfully applied to detect methane in the 8 μm spectral range [44][45][46], this method still relies on absorption lines with known frequencies for frequency calibration [44,47].…”

Coherently-Averaged Dual-Comb Spectrometer at 7.7 µm with Master and Follower Quantum Cascade Lasers

“…Mid-infrared (MIR) quantum cascade laser (QCL) frequency combs [2] are an appealing and thriving technology for DCS [3,4], as they cover strong spectroscopic absorption bands of many relevant molecules in the MIR region. Dual QCL comb spectrometers have become commercially available as a table-top instrument, which is leading to new discoveries in many fields of science including biology and chemistry [5][6][7][8][9][10][11][12]. One key advantage of QCL-based DCS is the ability to perform studies with up to sub-microsecond time-resolution [11].…”