Determination of the Size of Dielectric Particles Using White Light Spectroscopy

White light spectroscopy has the potential to be used as an effective optical method for determination of unknown sizes of scattering particles in the range of 2 to 15μm in diameter. The potential applications of this technique are for determination of cell-nuclei size of biological samples and air-born pollutants (pollutants' diameters of 2.5 and 10μm according to EPA standards). The proposed method uses backscattered light data that can be related to the size of the scatterer. The spatial backscattering spectra, in terms of scattered intensity versus wavelength, exhibit specific oscillation patterns, relating the number of oscillations to the morphology of the scatterer. Those oscillations are due to interference effects between light that is refracted and reflected through the particle surfaces. The number of peaks is linearly proportional to the scatterer size and by counting those peaks, one can simply estimate the scatterer's size. However this method is applicable only for individual scatterer sizes and has certain limitations. When looking at the spatial spectra of scatterers with diameters greater than 10μm, oscillations are becoming more complex and hard to count. Also when a mixture of different sized particles is investigated, the resulting spatial spectrum is not clear. By examining the white light spectrometer data in the Fourier domain, the frequency content of spatial spectrum can be explored. In addition by filtering the spatial spectra, individual frequency components can be selected, helping for precise estimation of the size of homogeneous scatterers and also for identification of the individual components of the mixed sample.;The work in this dissertation includes detailed theoretical and experimental comparisons using Mie scattering theory, in both the spatial and frequency domains. Experiments are performed on samples, made with polystyrene microspheres. Experimental and theoretical studies will be performed with respect to homogeneous and heterogeneous samples. The proposed work also includes validation of experimental studies in spatial and frequency domains. The primary goal of this work is to develop a procedure for determining the size of particles comprising an unknown sample.