Electromagnetic properties of complex media: Nano-structured semicontinuous films and fractal aggregates

The nonlinear optical properties of complex medium are extremely difficult to study due to the randomness of the underlying structure. Important members of the family of inhomogeneous systems are the metal-dielectric composites and fractal aggregates. Studies based on effective medium approach have shed some light on the macroscopic properties of those materials but only recently, due to the advances of computer technology, researchers were able for first time to study and ultimately understand their local electromagnetic response. In this work we develop new numerical and analytical methods that explain the effective and local electromagnetic properties of nano-structured materials. Specifically, we study the electromagnetic response of random metal-dielectric films and fractal aggregates in wide spectral range. The Surface Plasmon (SP) eigenvalue-eigenvector problem is solved and modifications of the eigenfunctions resulting from the current conservation are investigated. The theoretical findings are shown to be in excellent agreement with the experimental results. New analytical theory for the Surface Enhanced Raman Spectroscopy (SERS) of periodic and semi-periodic arrays of nanometer size metal particle is developed and checked with direct numerical calculations. Our study shows that under resonant conditions, periodic arrays can be superior in their non-linear properties when compared to random films and fractal aggregates. Numerical and analytical investigations of dielectric particles coated with semicontinuous film are performed. We propose an adiabatic photomodification of the optical response which is achieved through intensity modulated laser pulses. The absorption properties of mixtures of steroidal particles and conductive sticks are investigated in great details.