Browsing by Author "Jiang, Wenzhe"
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Item Hydrogen peroxide detection with quartz-enhanced photoacoustic spectroscopy using a distributed-feedback quantum cascade laser(AIP Publishing LLC., 2014) Ren, Wei; Jiang, Wenzhe; Sanchez, Nancy P.; Patimisco, Pietro; Spagnolo, Vincenzo; Zah, Chung-en; Xie, Feng; Hughes, Lawrence C.; Griffin, Robert J.; Tittel, Frank K.A quartz-enhanced photoacoustic spectroscopy sensor system was developed for the sensitive detection of hydrogen peroxide (H2O2) using its absorption transitions in the v6 fundamental band at ∼7.73 μm. The recent availability of distributed-feedback quantum cascade lasers provides convenient access to a strong H2O2 absorption line located at 1295.55 cm−1. Sensor calibration was performed by means of a water bubbler that generated titrated average H2O2vapor concentrations. A minimum detection limit of 12 parts per billion (ppb) corresponding to a normalized noise equivalent absorption coefficient of 4.6 × 10−9 cm−1W/Hz1/2 was achieved with an averaging time of 100 s.Item Quantum cascade laser based spectroscopic sensor systems for trace gas detection(2014-03-31) Jiang, Wenzhe; Tittel, Frank K.; Kelly, Kevin F.; Griffin, Robert J.Quantum cascade laser (QCL) based spectroscopic techniques are useful for the quantitative detection and monitoring of molecular trace gas species in the mid-infrared spectral region. Sensitive and selective trace gas detection can be realized by targeting distinct and strong absorption lines in the mid-infrared region with QCLs in this spectral region. Basic concepts of QCL based spectroscopic techniques are described. QCL based sensor systems are of interest for biomedical, environmental, and industrial applications utilizing various spectroscopic methods. This thesis describes the design, development and performance of three sensor systems. A tunable laser absorption spectroscopy (TLAS) based sensor system for nitric oxide detection was designed, which achieved a minimum detection limit of 505 pptv with a 1 second data acquisition time. A quartz enhanced photoacoustic spectroscopy (QEPAS) based H2O2 sensor system was implemented with a minimum detection limit of 12 ppbv with a 100 sec averaging time corresponding to a normalized noise equivalent absorption (NNEA) coefficient of 4.6×10-9 cm-1W/Hz-1/2¬. In addition, a QEPAS sensor system with capability of detecting both methane (CH4) and nitrous oxide (N2O) was developed and investigated. The measured minimum detection limits with a 1 second acquisition time of CH4 and N2O are 13 ppbv and 6 ppbv, respectively. The developed CH4/N2O QEPAS sensor was installed in a mobile laboratory operated by Aerodyne, Inc during a 2013 NASA DISCOVER_AQ field campaign to perform atmospheric CH4 and N2O measurements adjacent to two urban waste disposal sites in the Greater Houston urban area.Item Quantum cascade laser-based multipass absorption system for hydrogen peroxide detection(SPIE, 2015) Cao, Yingchun; Sanchez, Nancy P.; Jiang, Wenzhe; Ren, Wei; Lewicki, Rafal; Jiang, Dongfang; Griffin, Robert J.; Tittel, Frank K.Hydrogen peroxide (H2O2) is a relevant molecular trace gas species, that is related to the oxidative capacity of the atmosphere, the production of radical species such as OH, the generation of sulfate aerosol via oxidation of S(IV) to S(VI), and the formation of acid rain. The detection of atmospheric H2O2 involves specific challenges due to its high reactivity and low concentration (ppbv to sub-ppbv level). Traditional methods for measuring atmospheric H2O2 concentration are often based on wet-chemistry methods that require a transfer from the gas- to liquid-phase for a subsequent determination by techniques such as fluorescence spectroscopy, which can lead to problems such as sampling artifacts and interference by other atmospheric constituents. A quartz-enhanced photoacoustic spectroscopy-based system for the measurement of atmospheric H2O2 with a detection limit of 75 ppb for 1-s integration time was previously reported. In this paper, an updated H2O2 detection system based on long-optical-path-length absorption spectroscopy by using a distributed feedback quantum cascade laser (DFB-QCL) will be described. A 7.73-μm CW-DFB-QCL and a thermoelectrically cooled infrared detector, optimized for a wavelength of 8 μm, are employed for theH2O2 sensor system. A commercial astigmatic Herriott multi-pass cell with an effective optical path-length of 76 m is utilized for the reported QCL multipass absorption system. Wavelength modulation spectroscopy (WMS) with second harmonic detection is used for enhancing the signal-to-noise-ratio. A minimum detection limit of 13.4 ppb is achieved with a 2 s sampling time. Based on an Allan-Werle deviation analysis the minimum detection limit can be improved to 1.5 ppb when using an averaging time of 300 s.Item Simultaneous atmospheric nitrous oxide, methane and water vapor detection with a single continuous wave quantum cascade laser(The Optical Society, 2015) Cao, Yingchun; Sanchez, Nancy P.; Jiang, Wenzhe; Griffin, Robert J.; Xie, Feng; Hughes, Lawrence C.; Zah, Chung-en; Tittel, Frank K.A continuous wave (CW) quantum cascade laser (QCL) based absorption sensor system was demonstrated and developed for simultaneous detection of atmospheric nitrous oxide (N2O), methane (CH4), and water vapor (H2O). A 7.73-µm CW QCL with its wavelength scanned over a spectral range of 1296.9-1297.6 cm−1 was used to simultaneously target three neighboring strong absorption lines, N2O at 1297.05 cm−1, CH4 at 1297.486 cm−1, and H2O at 1297.184 cm−1. An astigmatic multipass Herriott cell with a 76-m path length was utilized for laser based gas absorption spectroscopy at an optimum pressure of 100 Torr. Wavelength modulation and second harmonic detection was employed for data processing. Minimum detection limits (MDLs) of 1.7 ppb for N2O, 8.5 ppb for CH4, and 11 ppm for H2O were achieved with a 2-s integration time for individual gas detection. This single QCL based multi-gas detection system possesses applications in environmental monitoring and breath analysis.