Resonance light scattering from a suspension of microspheres

Abstract

Intensity-vs-wavelength spectra of light scattered elastically from suspensions of monodisperse, dielectric microspheres were measured for both parallel and perpendicular polarizations. Whereas previous experimenters have observed sharp resonances in the spectra of single microspheres, the broad peaks observed in the present experiment are a summation of sharp resonances over the range of sizes present in the illuminated region of the suspension. Peak locations in these resonance light scattering (RLS) spectra were then compared with those computed from Mie theory to obtain a precise value for the mean diameter of the microspheres. The RLS-determined mean diameter of 9.90μm agreed to within 0.01 μm with the values measured by optical array sizing and scanning electron microscopy, both high-accuracy techniques. However, the shapes of the RLS spectra calculated for different size-distribution widths gave a standard deviation of 0.035 μm, less than half of the value obtained by array sizing and transmission electron microscopy. Mie scattering calculations for a range of mean diameters and distribution widths showed that the RLS method is useful for microsphere diameters from ~5μm to ~ 25μm, depending on the distribution width. Experimental procedures, computer analysis of the RLS spectra, sources of error, and limitations on the technique for high-accuracy microsphere sizing are discussed.