Study Of Thermal Properties Of Binary Solution By Coherent Light-induced Grating Method

Thermal diffusion still is the subject of today’s reasearch in view of its applications in energy, chemical engineering, semiconductor and other industries. The thermal diffusion of solution, polymer and colloid can be described by thermal diffusion coefficient, mass diffusion coefficient and soret coefficient. For the process of thermal diffusion is complexity and easy to be affected by external factors, it is important to choose a proper method for getting accurate parameters. Coherent light-induced grating method is based on two coherent light which is called write light and written in solution. It will generate perturbation, while another beam called readout beam is used to detect the process of thermal diffusion. Diffraction intensity reflects thermal diffusion phenomenon, so thermal diffusion coefficient and mass diffusion coefficient can be obtained by analyzing the diffraction intensity. Compared to traditional measurement methods, coherent light-induced grating method is characterized by fast measurement speed and high accuracy.Based on the theoretical model of heat transfer and mass transfer in binary solution, evolvement rule of modulation depth of temperature grating, concentration grating and refractive index grating in binary solution were analyzed under the action of write beams and in delay process. And the influence of parameters for modulation depth of each grating was analyzed quantitatively.Combined with theoretical and experimental analysis, we mainly studied of the thermal diffusion process of CS2-Ethanol solution mixed with methyl red dye. In theory, the modulation depth of temperature grating, concentration grating and refractive index grating and readout light’s diffraction intensity of first-order changing over time were numerically simulated. In experiment, choosing 532 nm laser as write light and 632.8 nm laser as readout light, we builded a coherent light-induced grating method optical experiment and the readout light’s diffraction intensity of first-order was collected. Theoretical results matched well with experimental results. According to the theory equation and experiment results, we fitted the thermal diffusion coefficient and mass diffusion coefficient of the sample solution, and contrasted the fitting results with the classical parameter.Besides, taking the double grating system composed by temperature grating and concentration grating as the research subject, we studied the evolvement rule of readout light’s intensity of first-order changing over time diffracted by temperature grating and concentration grating. Based on the theory of diffraction, the light intensity distribution diffracted by dynamic double grating was derived. We simulated the intensity of a plane wave’s zero-order diffraction light changing over time under the normal incidence condition and the small angle incidence condition. In experiment, optical system circuit was set up, and the intensity of zero-order diffraction light was collected, and the experimental results were contrasted with the theoretical results.At last, we applied the theory of double grating diffraction to the analysis of the experimental results got by coherent light-induced grating method. According to the theory of double grating diffraction, the readout light’s first-order diffraction intensity diffracted by temperature grating and concentration grating was obtained. It turned out that the results of numerical simulation by two different theoretical approach matched well with the experimental results, which provides theoretical support for the study of binary solution’s thermal properties by coherent light-induced grating method.