Light induced thermodiffusion in magnetic fluids

I. Turek¹ - J. Štelina¹ - C. Musil¹ - P. Kopċanský² - M. Koneracká² - M. Timko² - I. Potoċová² - A. Juríková² - Tomċo. L.³

¹ Department of Physics, University of Żilina, Veľký Diel, 010 26 Żilina, Slovakia
² Institute of Experimental Physics, Slovak Academy of Sciences, Watsonova 47, 043 53 Košice, Slovakia
³ Military Aviation Academy, Rampová 7, 041 21 Košice, Slovakia

Abstract
The influence of intensive periodic illumination of a magnetic fluid upon the temperature distribution and consecutive creation of diffraction gratings due to the temperature dependence on the refractive index, or the redistribution of colloidal particles (in colloidal liquids) due to the temperature gradient, is studied. The parameters of rise and decay of such gratings are calculated under a linear approximation and are compared with the parameters of gratings observed in magnetic fluids after intensive periodic illumination. The work presents also a simplified description of the phenomenon of structuralisation of the colloidal particles' concentration, which is caused by a nonlinearity present at intensive illumination of a colloidal fluid with a negative Soret constant. The existence of this phenomenon is documented by observation of structuralisation of optical transmittance caused by intensive illumination. The presented results of the second diffraction maximum observation indicate to the anharmonicity of created gratings, and so, to the presence of a non-linearity in the grating building process. Figs 5, Refs 4.