Experimental Study on the Forced Rayleigh Scattering Method using CO₂ Laser (1st Report, Development of the Free-Surface-Heating Technique and Preliminary Measurement of Molten Salts)

We have developed a new apparatus to measure the thermal diffusivity of liquids by the forced Rayleigh scattering method using a CO₂ laser. In the case of employing the infrared wavelength laser as a heating source, it is less necessary to add dye substances in samples than with the previously used Ar⁺ laser. The purpose of the present study is to develop a practical forced Rayleigh scattering apparatus applicable to a wide range of substances and conditions. In the present study, we have invented a free-surface-heating technique which does not require any cell windows. In order to demonstrate the applicability of the present apparatus without adding dye substances, we have preliminarily measured the thermal diffusivity of molten KNO₃ and a molten carbonate mixture (Li₂CO₃-Na₂CO₃-K₂CO₃=43.5-31.5-25.0 mol%) in the temperature range up to about 1000 K.