Abstract
Feasibility of a newly developed size determination method for sub-micron particles using multi-wavelength polarized lights is investigated, experimentally. According to the Mie's theory the polarization ratios of scattered lights are calculated numerically, which is a function of the particle diameter, the refraction index, and the wavelength of the incident light. Polystyrene particles are used as the test particles, which are suspended in purified water. The arithmetic mean diameters of them are varied from 0.356 to 0.77μm, which is measured with a centrifugal sedimentation method. In order to extend the measurement range of convestional polarization ratio methods, three kinds of He-Ne lasers, whose wavelengths are 543.5, 594.1, and 632.8nm, are used. The laser beams passes through the particles, and the scattered images are acquired with a digital CCD camera set in parallel and perpendicular directions to the polarization plane of the incident light. The polarization ratios of the scattered lights are estimated from these scattered light images, and the acquired data are compared with the analytical values. It is shown that, by use of the multi-wavelength polarization ratio method, the measurement range of the particle size can be extended up to the order of 1μm, and that the accuracy of the results lies from 0.1% to 7.6%, when compared with the results of a centrifugal sedimentation method.
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