基于量子级联激光器和长光程气室的甲烷传感器

根据中红外光谱吸收原理，利用甲烷(CH₄)气体分子在7.5 μm处的基频吸收特性，设计了一种基于量子级联激光器(QCL)和新型多反射长光程气体吸收气室(MPC)的甲烷气体传感器。该仪器使用了可进行热电冷却、工作在脉冲方式下、中心波长为7.5 μm的QCL，通过在室温条件下调节其注入电流(500 mA～1.6 A调节范围)，其出射光波长可以扫过CH₄(1 332.8 cm-1)气体吸收线。同时使用了一种紧凑型MPC(40 cm长，800 mL采样容积)，使得系统有效总光程达到16 m。此外，系统中使用了参考气室，并加入了空间滤波光学结构以满足MPC对入射光束的要求，配合差分吸收光谱检测原理，有效地改善了光束质量，降低了由光源波动引起的噪声，提高了仪器的检测灵敏度。通过对不同浓度的甲烷气体进行多次检测，该仪器的稳定性能良好，按信噪比为1计算，可实现对甲烷气体的检测下限为1 μmol·mol-1。

A Methane Gas Sensor Based on Mid-Infrared Quantum Cascaded Laser and Multipass Gas Cell

According to the principle of mid-infrared absorption spectrum,the fundamental absorption characteristics at the wavelength of 7.5μm of methane (CH4)molecule was used to design a mid-infrared quantum cascaded laser (QCL)and multi-pass gas cell (MPC)-based methane gas sensor.This sensor uses a thermoelectrically cooled,pulse mode QCL whose central wavelength is 7.5μm.The QCL wavelength was scanned over CH4 absorption line (1 332.8 cm-1 )through adjusting the injec-tion current under the condition of room temperature.Meanwhile,a compact MPC (40 cm long and 800 mL sampling volume) was utilized to achieve an effective optical path length of 16 meters.Additionally,a reference gas cell was occupied and joined a spatial filtering optical structure to meet the requirement of MPC in incidence beam,effectively improved the beam quality,re-duced the noise which is caused by the fluctuation of QCL and improved the detection sensitivity of this instrument under the guidance of differential optical absorption spectroscopy method.It indicated that the stability of this instrument is good by means of multiple measurements to the methane gas with different concentration,a detection limit of 1μmol·mol-1 will be obtained when the signal-to-noise ratio equals 1 .