Gas sensing using Quantum Cascade Lasers (QCLs) as a light source is expected to offer a high sensitivity, a short measurement time, and a good portability compared to conventional sensing methods. We have studied low power consumption 7 μm wavelength QCLs for realizing a portable sensing apparatus. The performance of our Distributed Feedback (DFB) QCL in gas sensing was evaluated by measuring the mid-infrared absorption spectrum. In this evaluation, a multi pass type gas cell was used for gas absorption, and for sweeping lasing wavelength of QCLs, the injection current of the DFB-QCL was swept. First, we measured the absorption spectrum of the room air, and found the absorption lines of water and methane to agree well with our simulation results. We then evaluated the sensitivity of the apparatus using a methane gas of a certain amount of concentration, and achieved a high sensing sensitivity of 17 ppb at a DFB-QCL power consumption of less than 3 W.
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