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This New Views article will highlight some recent advances in high sensitivity gas detection using direct infrared absorption frequency comb laser spectroscopy, with a focus on frequency comb use in chemical reaction kinetics and our own contribution to this field. Our recently implemented detection technique uses a combination of a 12.9 GHz free spectral range virtually imaged phased array and diffraction grating to spatially disperse the mid-infrared frequency comb onto a camera. Individual frequencies or ‘comb teeth’ of a 250 MHz repetition-rate frequency comb are able to be resolved. High molecular sensitivity is achieved by increasing the interaction path length using a Herriott multipass cell. High spectral resolution, broadband spectral coverage, and high molecular sensitivity are all achieved on an adjustable 1–50 µs timescale, making this frequency comb apparatus ideal for measuring chemical reaction kinetics where multiple absorbing species can be monitored simultaneously. This New Views article will also discuss some of the challenges and decisions that chemists might face in implementing this advanced physics technology in their own laboratory. Spatially dispersed 250 MHz mid-infrared frequency comb laser, with absorption of some frequencies by a dilute sample of methane. KEYWORDS: Frequency combs, chemical kinetics, trace gas detection
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GHz repetition rate mid-infrared frequency comb spectroscopy of fast chemical reactions
Molecular diagnostics are a primary tool of modern chemistry, enabling researchers to map chemical reaction pathways and rates to better design and control chemical systems. Many chemical reactions are complex, involving multiple species and reaction pathways occurring on µs or shorter timescales. Existing diagnostic approaches provide a subset of chemical and thermodynamic information. Here we optimize across many diagnostic objectives by introducing a high-speed and broadband, mid-infrared dual-frequency-comb absorption spectrometer. The optical bandwidth of >1000cm−1covers absorption fingerprints of many species with spectral resolution <0.03cm−1to accurately discern their absolute quantities. Key to this advance are 1 GHz pulse repetition rate mode-locked frequency combs covering the 3–5 µm region that enable a spectral acquisition rate of 290cm−1per 17.5 µs per detector forin situtracking of fast chemical process dynamics. We demonstrate this system to quantify the abundances and temperatures of each species in the complete reactants-to-products breakdown of 1,3,5-trioxane, which exhibits a formaldehyde decomposition pathway that is critical to modern low-temperature combustion systems. By maximizing the number of observed species and improving the accuracy of temperature and concentration measurements, this spectrometer provides a pathway for modern chemistry approaches such as combining chemical models with machine learning to constrain or predict complex reaction mechanisms and rates.
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- PAR ID:
- 10515382
- Publisher / Repository:
- Optical Society of America
- Date Published:
- Journal Name:
- Optica
- Volume:
- 11
- Issue:
- 6
- ISSN:
- 2334-2536
- Format(s):
- Medium: X Size: Article No. 876
- Size(s):
- Article No. 876
- Sponsoring Org:
- National Science Foundation
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