Multiple scattering of waves by dense random distributions of particles for applications in light scattering by noble metal nanoparticles and microwave scattering by terrestrial snow

Abstract

In this dissertation, the multiple scattering of waves by dense random distribution of particles is investigated. The Numerical Maxwell Model of three-dimensional simulations (NMM3D) is applied to solve the multiple scattering numerically. The positions of the particles are generated by the Monte Carlo method for both non-sticky particles and sticky particles. The simulation results are useful for applications in remote sensing related to terrestrial snow as well as nanotechnology. In the studies of the light scattering by noble metal nanoparticles, we show the scattering properties of such nanoparticles that exhibit plasmon resonance. We study adhesive nanoparticles and also extinction and absorption as a function of concentrations. Results indicate that the plasmon resonance can disappear for high concentration of nanoparticles. The bistatic scattering properties described by the phase matrix of the scattering of the nanoparticles is studied. A similar trend of Rayleigh scattering is obtained with also a dominant forward scattering. Presented results are based on Mie theory instead of the dipole approximation which is widely used in the studies of scattering by nanoparticles. With enough number of particles being included in the system, the results give a good estimation for scattering properties of huge number of nanoparticles. In the studies of microwave scattering by terrestrial snow, the results are presented for the co-polarization and cross polarization scattering phase matrices and the extinction coefficients of sticky particles. We consider concentrations of particles up to 40% by volume. Results of dense media simulations depart from the predictions based on classical theory of independent scattering which is applicable for very low concentrations. The simulation results (NMM3D) agree with those of the quasicrystalline approximation (QCA) for concentration up to 20%. However, they start to deviate from those of the QCA for higher concentrations as QCA underestimates the extinction. Simulations results also predict strong cross polarization in the phase matrix of densely packed spheres. This is the unique feature of NMM3D that is neither predicted by classical independent scattering nor by QCA.