Faculty of Engineering, Okayama University Acta Medica Okayama 0475-0071 27 1 1992 Measurement of Methane Concentration in a Rice Paddy Field with a Tunable Diode Laser Absorption Spectrometry 45 53 EN Naoki Kagawa Osami Wada Xu Hai Ryuji Koga Hiroya Sano Kazuyuki Inubushi A prototype device based on the tunable diode laser absorption spectrometry was constructed and the atmospheric methane concentration near the terrain in a rice paddy field was measured. An open optical path of 50 m length was employed along with a PbSnTe diode laser. Diurnal change of methane density with 30 seconds temporal resolution was recorded associated with meteorological parameters. A feasibility was proven for a practical application for in situ study of atmospheric methane. No potential conflict of interest relevant to this article was reported.

Faculty of Engineering, Okayama University Acta Medica Okayama 0475-0071 26 1 1991 Application of the Adjoint Spectrum to the Frequency Tracking in Spectrometry with Tunable Diode Lasers Suffering from Temperature Drift 43 49 EN Moncef Bouzidi Ryuji Koga Osami Wada Naoki Kagawa Megumi Kosaka A numerical technique called as "adjoint spectrum" has been proposed by the authors in a previous work. Two applications of it are presented here. It is demonstrated that by generalizing the aspect of adjoint spectrum it becomes possible to measure densities of mixed gases simultaneously. An experimental proof of this has been carried on and simultaneous measurement of densities of both methane and dinitrogen oxide was realized. On the other hand, it is also reported that frequency shifting of spectra, which is a cause of error in spectrometric measurements, can be corrected by exploiting the adjoint spectrum technique in connection with the Taylor expansion. Numerical examples showing the success of this method are reported as well. No potential conflict of interest relevant to this article was reported.

Faculty of Engineering, Okayama University Acta Medica Okayama 0475-0071 25 1 1990 Second Harmonic Detection of Atmospheric Trace Gases with a Train-Pulse Driven Lead-Salt Tunable Diode Laser for an Operation at Peltier Cooling Temperature 37 50 EN Moncef Bouzidi Ryuji Koga Osami Wada Naoki Kagawa Xu Hai Megumi Kosaka Hiroya Sano Is proposed a tunable diode laser absorption spectrometer system which employs a pulsed current to drive the diode laser still implementing a second-harmonic detection methods enhancing a signal to noise up to 104 times that the case without it. This system affords the lead-salt diode laser a higher operating temperature which allows a more compact deep cooling system. A principle is based on employing a gated integrator between the preamplifier and the lock-in amplifier. Investigations are made on the optimum selection of the gating aperture time interval as determined by response time of the infrared detector and the pulse width of the laser driving current. No potential conflict of interest relevant to this article was reported.