Browsing by Author "Li, Shangzhi"

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    Highly sensitive and selective CO sensor using a 2.33 μm diode laser and wavelength modulation spectroscopy
    (Optical Society of America, 2018) Cui, Ruyue; Dong, Lei; Wu, Hongpeng; Li, Shangzhi; Zhang, Lei; Ma, Weiguang; Yin, Wangbao; Xiao, Liantuan; Jia, Suotang; Tittel, Frank K.
    A ppm-level CO sensor based on a 2f wavelength modulation spectroscopy (2f-WMS) technique was developed for the application of SF6 decomposition analysis in an electric power system. A detailed investigation of the optimum target line selection was carried out to avoid spectral interference from high purity SF6 in a wide wavelength range. A diode laser emitting at 2.33 μm and a 14.5-m multipass gas cell (MGC) was employed to target the R(6) line of the CO first overtone band and increase the optical path, respectively, thus resulting in a minimum detection sensitivity of 1 ppm. A Levenberg-Marquardt nonlinear least-squares fit algorithm makes full use of the information from all data points of the 2f spectrum and as a result, a measurement precision of ~40 ppb was achieved with a data update rate of 0.6 s. The sensor performance was also evaluated in terms of the gas flow rate, stability, and linearity. The results showed that the best operating condition with a precision of 6 ppb can be achieved by increasing the gas flow rate to the value that matches the optimum averaging time of 48 s.
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    Piezo-enhanced acoustic detection module for mid-infrared trace gas sensing using a grooved quartz tuning fork
    (Optica Publishing Group, 2019) Li, Shangzhi; Li, Shangzhi; Wu, Hongpeng; Wu, Hongpeng; Cui, Ruyue; Cui, Ruyue; Sampaolo, Angelo; Patimisco, Pietro; Spagnolo, Vincenzo; Spagnolo, Vincenzo; Spagnolo, Vincenzo; Tittel, Frank K.; Dong, Lei; Dong, Lei
    A grooved quartz tuning fork (QTF) with a prong spacing of 800 µm for QEPAS application is reported. The prongs spacing is large enough to facilitate optical alignments when a degraded laser beam is used for QEPAS-based trace gas sensors. The grooved QTF has a resonance frequency of 15.2 kHz at atmospheric pressure and is characterized by four rectangular grooves carved on the QTF prong surfaces. With a grooved-prong, the electrical resistance R of the QTF is reduced resulting in an enhanced piezoelectric signal, while the Q factor is not affected, remaining as high as 15000 at atmospheric pressure. The geometric parameters of the acoustic micro resonators (AmRs) for on-beam QEPAS were optimized to match the grooved QTF, and a signal-to-noise gain factor of ∼ 30 was obtained with an optimum configuration. The performance of the QEPAS-based sensor was demonstrated exploiting an interband cascade laser (ICL) for CH4 detection and a 1σ normalized noise equivalent absorption (NNEA) coefficient of 4.1×10−9 cm−1 W/√Hz was obtained at atmospheric pressure.