Dual-comb spectroscopy for high-temperature reaction kinetics

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-C3H4/18% O2/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, , of 9.86 GHz and a difference in comb spacing, Δ , 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.

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

“…As recently shown, near-IR dual-comb spectroscopy is well-suited for many major species in combustion diagnostics in single-pass arrangements [23]. With the development of compact and electrically pumped mid-IR QCL combs, the spectroscopically attractive MIR spectral range becomes increasingly accessible [24][25][26]. As a consequence, the field of QCL-based frequency-comb spectroscopy grows rapidly, resulting in a variety of promising applications [26][27][28], including recent shock-tube studies using a QCL DCS in the spectral range of 1200 cm −1 [26,28].…”

“…With the development of compact and electrically pumped mid-IR QCL combs, the spectroscopically attractive MIR spectral range becomes increasingly accessible [24][25][26]. As a consequence, the field of QCL-based frequency-comb spectroscopy grows rapidly, resulting in a variety of promising applications [26][27][28], including recent shock-tube studies using a QCL DCS in the spectral range of 1200 cm −1 [26,28]. In the current work, we use recently developed QCL-based frequency combs [29], specifically tailored for accessing the spectral range of 1740-1790 cm -1 with QCL DCS for the first time.…”

Broadband Time-Resolved Absorption and Dispersion Spectroscopy of Methane and Ethane in A Plasma Using a Mid-Infrared Dual-Comb Spectrometer

“…Similar to traditional FTS, the interferogram is recorded using a single-point detector and the absorption spectrum is achieved by a Fourier transformation of the recorded interferogram. Due to its inherent short measurement time, mid-infrared DCS have received increasing attention in various applications such as combustion diagnostics [25][26][27], study of protein dynamics [28], radicalradical interactions in flash photolysis mixtures [29], and DC/pulsed plasma discharges [30].…”

Simultaneous determination of transient free radicals and reaction kinetics by high-resolution time-resolved dual-comb spectroscopy

“…In recent years, direct frequency comb spectroscopy (DFCS) techniques [6][7][8][9][10][11] , which enable high resolution, rapid, and broadband measurements, have been developed for different spectral regions and used in various applications. Time-resolved spectroscopy based on DFCS methods has been used for monitoring spectral variations under flash photolysis 12 , electric discharge 13 , laser-induced plasma 14,15 , and combustion conditions 16 as well as for studying gas-phase reaction kinetics [17][18][19] , protein dynamics 20 , and population relaxation processes 21 . In particular, timeresolved DFCS methods can be demonstrated in the midinfrared (MIR) region to achieve sensitive molecular identification and quantitation 12,13,[17][18][19][20] .…”

“…Time-resolved spectroscopy based on DFCS methods has been used for monitoring spectral variations under flash photolysis 12 , electric discharge 13 , laser-induced plasma 14,15 , and combustion conditions 16 as well as for studying gas-phase reaction kinetics [17][18][19] , protein dynamics 20 , and population relaxation processes 21 . In particular, timeresolved DFCS methods can be demonstrated in the midinfrared (MIR) region to achieve sensitive molecular identification and quantitation 12,13,[17][18][19][20] . For instance, a MIR virtually imaged phased array (VIPA) spectrometer with a spectral coverage of 65 cm −1 and an optical resolution of 1 GHz (approximately 0.033 cm −1 ) has been employed for studying the OD + CO reaction and recording the vibrational spectra of DOCO radicals 12,17,18 .…”