A Broad Perspective: Advancing gas-sensing applications of mid-infrared supercontinuum sources

This dissertation investigates novel gas-sensing applications using broadband mid-infrared supercontinuum sources in combination with Fourier-transform spectroscopy. By leveraging the broad spectral coverage and high brightness of fiber-based and intrapulse difference-frequency generation (IDFG)-based supercontinuum sources, this work enables sensitive, multi-species detection across a range of real-world applications. Fiber-based supercontinuum sources are applied to study plasma-driven methane conversions, providing both quantitative product analysis and insights into plasma dynamics through in-situ measurements. Furthermore, an IDFG-based source is introduced with unprecedented spectral coverage (2–11.5 µm), enabling simultaneous detection of many molecular species, including molecular hydrocarbons (e.g., CH4, C2H4), oxides (e.g., SO2, NOx), and small organic molecules (e.g., acetone, ethyl acetate). This light source is used in the field deployment of a novel open-path spectroscopy system to monitor the emissions of, among others, greenhouse gases over a wastewater treatment plant. The dissertation also addresses the increasing complexity of spectral data analysis and proposes a systematic workflow for accurate quantification of known and unknown molecular species in complex mixtures. Finally, mid-infrared supercontinuum-based spectroscopy is extended to human breath analysis, demonstrating its potential for (un)targeted, non-invasive health diagnostics. Overall, this work showcases the versatility, sensitivity, and field applicability of supercontinuum-based gas sensing and positions it as a promising tool to address societal challenges related to climate, environment, and health.