Temporal Evolution of Thermal Diffusion Forced Rayleigh Scattering in Solution

• Main Authors: Chen, Yujun, 陳鈺鈞
• Other Authors: Wei, Taihuei
• Format: Others
• Language: zh-TW
• Published: 2011
• Online Access: http://ndltd.ncl.edu.tw/handle/14513463511974163730

碩士 === 國立中正大學 === 物理學系暨研究所 === 99 === In this thesis, we use the thermal diffusion forced Rayleigh scattering technique (TDFRST) to investigate thermal diffusion of two transparent liquids mixed together. In the experimental aspect, we use two 17 mW CW Nd:YVO4 laser beams at 532 nm as the writing beams to create interference patterns in the liquid mixture samples. In order to yield thermally induced phase grating, we add a small fraction of methyl red in the liquid mixture as the light absorber. Afterwards, we use a 5 mW CW HeNe laser beam as the read beam and send it to the grating at an angle satisfying the Braggs diffraction condition. By measuring the power of the read beam diffracted by the grating as a function time, we investigate thermal diffusion of the liquid mixture. In the theoretical aspect, we consider the write beams excite methyl red molecules in the intensity grating. Non-radiative relaxation of these excited molecules releases heat to the surrounding liquid molecules and thus yields a temperature grating lying on top of the write beam intensity grating. Afterwards, the temperature gradient, pointing from the constructive to the destructive regions of the intensity grating, drives the mass transport of each kind of the liquid molecules and methyl red molecules. Periodic distributions of the concentration of the liquids and methyl red produce a phase grating which diffracts the read beam. Measurement of the diffracted beam power as a function of time helps to explore the dynamic process of solute migration.