Mechanical Engineering Program, Physical Science and Engineering Division, Clean Combustion Research Center, King Abdullah University of Science and Technology (KAUST), 23955-6900, Thuwal, Saudi Arabia.
Sci Rep. 2023 Jan 28;13(1):1573. doi: 10.1038/s41598-023-28668-z.
A mid-infrared laser-based sensor is reported for the quantification of fugitive methane emissions. The sensor is based on a distributed feedback inter-band cascade laser operating near 3.3 μm. Wavelength tuning with cepstral analysis is employed to isolate methane absorbance from (1) fluctuations in the baseline laser intensity, and (2) interfering species. Cepstral analysis creates a modified form of the time-domain molecular free-induction-decay (m-FID) signal to temporally separate optical and molecular responses. The developed sensor is insensitive to baseline laser intensity imperfections and spectral interference from other species. Accurate measurements of methane in the presence of a representative interfering species, benzene, are performed by careful selection of the scan index (ratio of laser tuning range to spectral linewidth) and initial and final time of m-FID signal fitting. The minimum detection limit of the sensor is ~ 110 ppm which can be enhanced with an optical cavity. The proposed sensing strategy can be utilized to measure methane leaks in harsh environments and in the presence of interfering species in environment-monitoring applications.
一种基于中红外激光的传感器被用于定量测量逸散性甲烷排放。该传感器基于工作在近 3.3μm 的分布式反馈级联激光器。采用倒频谱分析进行波长调谐，以将甲烷吸收与（1）激光强度基准线的波动和（2）干扰物质分离开来。倒频谱分析生成了一种对时间域分子自由感应衰减（m-FID）信号的修正形式，以便在时间上区分光学和分子响应。所开发的传感器不受基准线激光强度不完美和其他物质光谱干扰的影响。通过仔细选择扫描指数（激光调谐范围与光谱线宽之比）以及 m-FID 信号拟合的初始和结束时间，可对存在代表性干扰物质苯的甲烷进行精确测量。该传感器的最小检测限约为 110ppm，可通过光学腔进行增强。该传感策略可用于在恶劣环境中测量甲烷泄漏，以及在环境监测应用中存在干扰物质的情况下进行测量。
