JaLCDOI 10.18926/15776
FullText URL Mem_Sch_Eng_OU_15_2_79.pdf
Author Koga, Ryuji| Nagase, Satoru| Kosaka, Megumi| Sano, Hiroya|
Abstract A method to monitor atmospheric gas concentration employing a tunable diode laser is proposed. An apparatus was built and experiments were made. The tunable diode laser employed was of'PbSnTe with its wavenumber about 1200 cm(-1) at a temperature of 77 K. Methane concentration in laboratory atmosphere was measured on the experiments. The inquired gas-density is obtained by a hardwired microcomputer incorporating the measured absorption spectrum over a prescribed range instead of an absorption at a single wavenumber. By this, drift type noises are suppressed. After an analysis based on experimental data, an attainable sensitivity for methane was found to be 1 ppb.m. This value may increase if an etalon fringe interference exists. The natural concentration, about 1 ppm, of atmospheric methane was actually measured with a short optical path of only one meter.
Publication Title Memoirs of the School of Engineering, Okayama University
Published Date 1981-03-30
Volume volume15
Issue issue2
Start Page 79
End Page 92
ISSN 0475-0071
language 英語
File Version publisher
NAID 120002307246
JaLCDOI 10.18926/15756
FullText URL Mem_Sch_Eng_OU_15_1_47.pdf
Author Koga, Ryuji| Nagase, Satoru| Kosaka, Megumi| Sano, Hiroya|
Abstract Basic prohlems are discussed about a local, realtime and very sensitive air-pollution monitoring using a laser diode. The method employs the second derivative spectrometry replacing the incoherent light source and mechanical choppers in a traditional method with the laser diode and a newly developed electronic system. Etalon fringes at this system becomes the dominant noise source and its statistic and dynamical features are to be understood. Numerical examination was done for the optimal width of optical frequency modulation. A very fast measurement of weak absorption spectra became possible by the development of lock-in-amplifiers with finite integration time instead of a low-pass filter. Spectra of methane in 7.6 μm region and a time-dependent spectrum of the etaIon fringe are shown.
Publication Title Memoirs of the School of Engineering, Okayama University
Published Date 1980-11-29
Volume volume15
Issue issue1
Start Page 47
End Page 60
ISSN 0475-0071
language 英語
File Version publisher
NAID 120002307627