Open-path Quantum Cascade Laser-based System for Simultaneous Remote Sensing of Methane, Nitrous Oxide, and Water Vapor Using Chirped-pulse Differential Optical Absorption Spectroscopy

摘要

Methane and Nitrous Oxide are long-lived greenhouse gases in the atmosphere with significant global warming effects. We report on application of chirped-pulsed quantum cascade lasers (QCLs) to simultaneous measurements of these trace gases in both open-path fence-line and backscatter systems. The intra-pulse thermal frequency chirp in a QCL can be time resolved and calibrated to allow for high resolution differential optical absorption spectroscopy over the spectral window of the chirp, which for a DFB-QCL can be reach ～2cm~(-1) for a 500 nsec pulse. The spectral line-shape of the output from these lasers are highly stable from pulse to pulse over long period of time (＞ 1 day), and the system does not require frequent calibrations.