To better understand the sources and sinks of atmospheric greenhouse gases and other trace gases, real-time and in-site monitoring of their atmospheric concentration change is essential in developing atmospheric models for a scientific understanding of atmospheric chemistry and environmental change. Global warming and climate change are two current key issues to all countries in the world. Compared to traditional WMS technique-based semiconductor photodetectors, the room-temperature QCTF-based WMS shows significant advantages of super-broadband wavelength response, much cheap and tiny. Improvements in sensitivity and detectivity can be significantly achieved by using laser sources with higher output power. Primary laboratory results indicate that an excellent linearity response of CH 4 concentration and optical power levels are founded, and a detection limit of 64 ppm is achieved with a 1-s averaging time, which can be further improved to 9 ppm at an optimal integral time of 250 s. For signal processing, a fast and effective signal analysis method based on the fast Fourier transform (FFT) algorithm is proposed for extracting the absorption intensity signal of the QCTFES-WMS, instead of a lock-in amplifier used for harmonic signal demodulation in traditional QCTF-based detection techniques. To explore the capabilities of this technique, a near-infrared (NIR) diode laser emitting at 1,653 nm and a QCTF-based photoelectric detector are developed for measuring trace methane (CH 4). In this paper, a gas sensing technique based on quartz-crystal-tuning-fork-enhanced spectroscopy (QCTFES) and wavelength modulation spectroscopy (WMS) is reported. 2Laser Spectroscopy and Sensing Laboratory, Anhui University, Hefei, China.1Chongqing Engineering Laboratory for Detection, Control and Integrated System, Chongqing Technology and Business University, Chongqing, China.Guangxiang Yang 1, Linguang Xu 2, Hua Liang 1 and Jingsong Li 2 *
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