Mid-Infrared Quantum Cascade Laser-Based Wavelength Modulation Spectroscopy for the Detection of Greenhouse Gases and NOx

We present a calibration-free R<inf>1f</inf>/ΔI<inf>1</inf> wavelength modulation spectroscopy (WMS) technique using mid-infrared quantum cascade lasers (QCLs) for highly sensitive, in-field measurements of nitric oxide from vehicular exhaust, ambient methane and ambient carbon dioxide. The nitric oxide absorption line at 5265.92 nm is targeted using a 5257 nm QCL, while the methane and carbon dioxide absorption lines at 7842.73 nm and 4319.3 nm are targeted using 7822 nm and 4320 nm QCLs respectively. This method enables precise, real-time monitoring of key greenhouse gases and pollutants in challenging environmental conditions.