Sensitivity Enhancement of Atmospheric-Gas Analysis with Lead-Salt Diode Laser through Spectral Data Processing

  • SANO Hiroya
    Department of Electronics, School of Engineering, Okayama University
  • KOGA Ryuji
    Department of Electronics, School of Engineering, Okayama University
  • KOSAKA Megumi
    Department of Electronics, School of Engineering, Okayama University

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Other Title
  • スぺクトル処理による高精度鉛塩半導体レーザー大気ガス分析の精度向上

Description

A very high sensitivity was obtained for only a 1.4 m optical path. A tunable Pb Sn Te diode laser of 7.6μm band was employed. Etalon fringes, which are dominant optical noises, were suppressed with using off-axis parabolic mirrors as beam-collimating elements along with a wedged window. Methane spectrum of a magnitude of 5×10-5 in absolute absorption were measured though being subject to random noise and base-line distortion both greater than the methane spectrum. A spectral data processing based on the notion of the adjoint spectrum successfully deduced densities of atmospheric methane every 10 seconds over one hour. Anrms fluctuation of the results was 0.1 ppm for about an 1 ppm average value.

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