Mid-infrared gas sensing using uncooled quantum cascade laser with low power consumption

Mid-infrared sensing with a Quantum Cascade Laser (QCL) as a light source is expected to offer a high sensitivity, a short measurement time, and a good portability compared to conventional methods. However, commercially available QCLs have high power-consumption, leading to the necessity for a large cooling system. Therefore, a portable sensor using a QCL have not been realized. To address this issue, recently we had developed a low power-consumption DFB-QCL which enables continuous wave (CW) operation up to 80 °C. In this study, we performed gas sensing using our QCL mounted on a Φ 5.6 mm TO-CAN package under uncooled condition. For example, even when the package temperature rose to room temperature +18 °C by injecting 180mA current (1.9 W power-consumption) into the uncooled QCL, it could CW operation, and emit output power of 9 mW. Lasing wavelength were stable when the power consumption of the QCL was below 2.2 W, and in this stable wavelength range, about 20 nm wavelength tuning range was obtained by sweeping injection current. We performed mid- infrared gas sensing of methane around 7.4 μm wavelength using a measurement system consisting of the QCL, a gas cell and a thermopile. For this measurement, the QCL was kept uncooled and was driven by CW current, which made a lasing wavelength sweep sufficient for sensing possible. Measured absorption wavelength, intensity, and width under uncooled operation were agreed well with the HITRAN simulation. Sensitivity was obtained about 2.3 ppb under uncooled operation, which was comparable to under cooled operation.