Frequency modulation laser spectroscopy method for methane isotopologue ratio and total concentration measurements at 1661 nm

Source identification and accurate measurements of methane gas concentration are key tools necessary for climate change management. Here we present a method for methane isotopologue ratio measurement using a laser-based frequency modulation (FM) spectroscopy technique in the near infrared at 1661 nm. We provide line shape analysis and discuss a fitting algorithm for accurate isotopologue ratio metrology and investigate and minimize the effects of residual amplitude modulation on the experimentally produced FM signal line shape. This FM technique is further evaluated for future development of a cavity-enhanced and noise-immune system capable of isotopologue ratio as well as ultrasensitive trace gas measurements, all accessible using a single distributed feedback laser.& COPY; 2023 Optica Publishing Group

Automated summary

This paper presents a method for measuring methane isotopologue ratio using laser-based frequency modulation spectroscopy in the near infrared. The authors discuss a fitting algorithm for accurate ratio measurements and ways to minimize the effects of residual amplitude modulation. The technique shows promise for developing a system capable of measuring isotopologue ratios and ultrasensitive trace gas concentrations.