Development of Highly Sensitive Infrared Laser Image Sensing Technique and its Application

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The purpose of the research is to design and develop a highly sensitive infrared remote imaging system for detecting concentration and distribution profile of air pollution and hazard leak gases using the infrared tunable parametric oscillator. We have achieved several major results for realizing high sensitive imaging performance of the system.(1)The optical parametric oscillator has been developed using the ring cavity resonator and infrared output was generated at 3.39μm infrared wavelength for matching to the absorption lines of methane gas. Tunable single frequency output was obtained by injection seeding the 1.55 μm signal wave with the tunable laser diode and the infrared idler spectrum width was narrowed to 1/300 of the free running oscillation width. High resolution absorption spectrum has been obtained for the methane molecule and realized minimum detectable density and column length product of 20 ppm・m.(2)The frequency upconverter has been designed using the periodically pol … More ed PPMgLN crystal with the intense pump beam and the infrared signal is converted to near infrared wavelength at 810nm and detected by a sensitive photomultiplier. The conversion efficiency of the upconverter was 40% for the backscatter signal and the detection sensitivity was 11 times higher than the cooled InAs detector.(3)By raster scanning the infrared beam with two scanner mirrors, imaging was realized for the methane gas plume with accuracy of 20 ppm・m at range of 〜2m. The infrared beam wavelength was alternately modulated to on and off absorption line of the methane gas and the differential absorption technique was used to obtain pure methane gas image.From these results, we could realize highly sensitive imaging system of distribution profile of methane leak gas. By further reducing the size and improving the pulse repetition frequency of the pump laser, the system can be used for practical application of remote detection of several pollution gases and hazard leak gases in the atmosphere. Less