为了对痕量甲烷(CH4)进行非接触式检测, 采用可调谐二极管激光吸收光谱(TDLAS)与波长调制光谱(WMS)的检测技术, 利用CH4位于中红外波段1 332.8 cm-1吸收谱线, 设计并研制出痕量CH4检测仪。 该仪器使用中心波长为 7.5 μm的中红外量子级联激光器(QCL), 通过调谐系数-0.2 cm-1·A-1, 采用固定工作温度调节其注入电流(0.6～1.6 A)的方式使其发光光谱扫描CH4气体吸收谱线(1 332.8 cm-1)。 在光学结构方面, 该仪器采用光程为76 m的herriott长光程密闭气体吸收气室, 配合差分检测光路, 降低了由激光光源波动引起的噪声, 确保对痕量CH4进行检测。 实验中, 实现了40×10-9最低检测下限, 检测结果的相对误差为0.09%, 稳定度优于2.8%, 验证了该仪器的可行性。

In order to detect trace methane (CH4) with non-contact method, a trace CH4 detector is designed and developed with the combination of tunable diode laser absorption spectroscopy (TDLAS) and wavelength modulation spectroscopy (WMS) detection technology, using the absorption line (1 332.8 cm-1) of CH4 in mid-infrared band. The instrument uses mid-infrared quantum cascaded laser (QCL) with centre wavelength at 7.5 μm, and uses the method of changing the injecting current (0.6～1.6 A) of QCL with fixed working temperature to make the emission wavelength of QCL to scan the methane’s absorption line (1 332.8 cm-1) via tuning parameters 0.2 cm-1·A-1. In terms of optical structure, the instrument using a gas absorption sealed herriott cell with 76 m long optical path, cooperating with difference detection optical path, reduces the noise which caused by the fluctuation of QCL, and guarantees the detection of trace CH4. In the experiment, we adopted minimum mean square error criterion to fit the relationship between methane concentration and harmonic peak signal. In addition, the minimum detection limit is 40×10-9, and the relative error of test results is 0.09%., The stability is better than 2.8%, which verify the feasibility of the instrument.