Hiroya Sano

Field methane tracking with a portable and real-time open-gas monitor based on a cw-driven Pb-salt diode laser

Abstract An atmospheric gas monitor with a PbSnTe diode laser has been developed. The open, 1 m optical path in a single-folded configuration enables local and non-contact measurement in a portable instrument. The accuracy is dependent on optical noise and a technique in diode-current modulation was effective in suppressing it. Analysis of the system noise based on the experimental data was made and a 10 ms interval was sufficient to attain an accuracy of 3 ppm for methane. Field measurements were made and a rapid fluctuation in the density of atmospheric methane density was recorded.

Analytical Description of Tunable Diode Laser Derivative Spectrometry

The instrument functions are investigated, and a quantitative description is given of how a second-derivative spectrometer employing a tunable diode laser attains the power to suppress spectral noise. As a result, it is found that the power can be improved by modifying the source-frequency modulation profile. The essence of this approach is to make the profile at its extreme as sharp as possible, and a hyperbolic sine profile with suitable parameters is proposed as the optimal profile that can be attained in practice.

High Sensitivity Short-Path Monitoring of Trace Gases Employing PbSnTe Tunable Diode Laser

A system for atmospheric trace gas monitoring is described. The absorption spectrum in the infrared region of a specific gas is involved. A lead-salt diode laser is employed for the tunable light source and the short optical path of less than one meter allows the equipment to be portable. Fast measurement can be performed thanks to be built-in microcomputer and specially developed electronic system. Reliability is achieved because a correlational algorithm is calculated by the computer avoiding the ambiguity of the absolute laser frequency. Gas-density data is obtained every few seconds. Experiments were executed for methane and a sensitivity of 0.3 ppmm with S/N=1 was attained being limited by parasitic etalon fringes. A higher sensitivity down to 0.01 ppmm is possible provided that a transversally mono-modal laser is employed.

In Situ and Real-Time Measurement of Methane Concentration in Rice Paddy Field at Okayama University Using Tunable Diode Laser Absorption Spectrometry

A transportable device based on absorption spectrometry was constructed and the atmospheric methane concentration over a rice paddy was measured. An open optical path of 50 m length was employed along with a PbSnTe diode laser. Diurnal change of methane concentration was recorded in association with meteorological parameters. Feasibility was proven for practical application to in situ study of atmospheric methane.

Orthogonally-Multiplexed Optical-Fiber Bus for High-Immunity Data Transmission

A directionaily coupling optical-fiber data bus using orthogonal multiplexing is presented for interconnection between multiple equipments in the presence of EMI. The experimental bus is for 8-channel 125-kb/s transmission. The bus line is made of plastic fiber and the correlator operates digitally. The undesired signals are rejected and the BERs are below about 1 *10 in the presence of such additive impulsive noise as SNRaO dB.