Development of the forced Rayleigh scattering method with CO_2 laser

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The results obtained from the present research project are summarized as follows.1. An apparatus to measure the thermal diffusivity of wide variety of substances without adding the dye material using CO_2 laser by the forced Rayleigh scattering method was developed. The characteristics of the apparatus is that the grating period can be adjustable from 20 mum to 300 mum and laser beam can be irradiated not only from horizontally but vertically on the sample.2. In order to confirm that this apparatus can be applicable to liquids, we measured thermal diffusivity of toluene and water using 7-nSe cell windows. We found the optimum measuring conditions through experimental examinations by changing adjustable parameters such as grating period, sample thickness and heating time.3. We developed the free surface heating method which does not require the cell windows. It was verified that this method has the advantage when the method is applied to high temperature conditions.4. The error factors (the beam off-center problem and sample thickness) were experimentally investigated.5. Thermal diffusivity of the mixture of Li_2CO_3-Na_2CO_3-K_2CO_3 = 41.5 : 31.5 : 25.0 mol% was measured using sapphire glass cell in the temperature range from 677 K to 970 K with the reproducibility of +^^-10%.