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 (CH 4 ) and Carbon Dioxide (CO 2 ) 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 CH 4 and 4317–4322 nm (2316.42–2313.74 cm −1 ) for CO 2 . Measurements conducted for CH 4 concentrations of 1300 and 480 ppm, and for CO 2 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 CH 4 at the 7673.83 nm absorption line and 9 ppm for CO 2 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%.