Self-mixing detection of methane and carbon dioxide using mid-infrared quantum cascade lasers.

We explore the use of self-mixing schemes based on Quantum Cascade lasers (QCLs) for the identification of greenhouse gases such as Methane (CH4) and Carbon Dioxide (CO2) in the mid-infrared (Mid-IR) region. In self-mixing, a QCL plays the role of the excitation source and the detector, thus eliminating the need for a dedicated cooled Mid-IR detector, reducing the cost and power consumption of the system. The experiments were performed within the spectral windows of 7669-7678 nm (1303.95-1302.42 cm-1) for CH4 and 4317-4322 nm (2316.42-2313.74 cm-1) for CO2. Measurements conducted for CH4 concentrations of 1300 and 480 ppm, and for CO2 concentrations of 430 ppm, 300 ppm and 200 ppm. After the calibration on our system, experiments took place that indicated a minimum detectable concentration of 45 ppm for CH4 at the 7673.83 nm absorption line and 9 ppm for CO2 at the 4319.78 nm absorption line, which are comparable to detector-based schemes. Additionally, a separate validation experiment demonstrated measurement accuracy of at least 90%.