Browsing by Author "Hu, Yinqiu"

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    A Sensitive Carbon Dioxide Sensor Based on Photoacoustic Spectroscopy with a Fixed Wavelength Quantum Cascade Laser
    (MDPI, 2019) Qiao, Shunda; Qu, Yanchen; Ma, Yufei; He, Ying; Wang, Yao; Hu, Yinqiu; Yu, Xin; Zhang, Zhonghua; Tittel, Frank K.
    A photoacoustic spectroscopy (PAS) based carbon dioxide (CO2) sensor with a fixed wavelength quantum cascade laser (FW-QCL) was demonstrated. The emission wavelength of the FW-QCL at 4.42 μm in the mid-infrared spectral region matched a fundamental CO2 absorption line. Amplitude modulation of the laser intensity was used to match the resonant photoacoustic (PA) cell. The noise from the background was reduced with the correlation demodulation technique. The experimental results showed that the sensor had excellent signal stability and a concentration linear response. When the integration time was 1 s, a 1σ minimum detection limit (MDL) of 2.84 parts per million (ppm) for CO2 detection was achieved. The long-term stability of the sensor was evaluated by means of an Allan deviation analysis. With an integration time of ~100 s, the MDL was improved to 1 ppm. This sensor was also used to measure the CO2 concentration from some common emission sources, such as cigarette smoking, automobile exhaust, and the combustion of some carbon-containing materials, which confirmed the stability and robustness of the reported FW-QCL based CO2-PAS sensor system.
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    Trace gas sensing based on multi-quartz-enhanced photothermal spectroscopy
    (Elsevier, 2020) Ma, Yufei; Hu, Yinqiu; Qiao, Shunda; He, Ying; Tittel, Frank K.
    A multi-quartz-enhanced photothermal spectroscopy (M-QEPTS) based trace gas detection method is reported for the first time. Different from traditional QEPTS sensor employing a single quartz tuning fork (QTF) as a photothermal detector, two QTFs were used in M-QEPTS to increase the signal amplitude by adding the generated piezoelectric signals. The coating film of the QTFs was removed in order to improve the laser absorption and transmission. Acetylene (C2H2) was chosen as the target analyte. Wavelength modulation spectroscopy (WMS) and 2nd harmonic detection were utilized for the concentration detection. Limit of detection (LoD) of 0.97 ppm was achieved with a 1 second integration time for the M-QEPTS sensor, which realized a 1.51 times signal enhancement compared to a traditional QEPTS sensor employing a single QTF. By using an Allan deviation analysis approach, LoD of 0.19 ppm for an optimum integration time of 200 s was obtained.