Optical properties of metal-dielectric composites

In Chapter 1, nonlinear optical properties of silver colloidal aggregates are studied. The real and imaginary parts of the cubic susceptibility of silver colloid aggregates are measured. It is found that the coefficient of nonlinear absorption strongly depends on the laser wavelength and intensity. Optical limiting effect in fractal silver colloids is observed. It is shown experimentally that the enhanced optical nonlinearity of aggregated metal colloids is connected with an enhancement of the local field in resonant domains of large clusters. The enhancement factor of the nonlinear absorption in aggregated silver colloids is about 700 as compared with nonaggregated samples.; In Chapter 2, nonlinear optical properties of Au nanoparticles created by ion implantation, are under investigation. Nondegenerate forward four-wave mixing technique is used to measure the third order nonlinear susceptibility for composite materials with Au nanocrystals formed inside a SiO₂ glass matrix. The Au nanocrystals are formed by the ion implantation and annealing method that produces very high volume fraction of nanoparticles. Large value of |χ(3)| has been measured to be ∼1.3 × 10 −7 esu. Two characteristic relaxation times, 5.3 ps and 0.66 ps, are estimated from the detuning curve of |χ(3)| and discussed using different models.; In Chapter 3, localization of optical excitations and selective photomodification are studied experimentally in fractal aggregates of silver colloidal nanoparticles. The localized optical excitations of the fractal colloids cover a broad spectral range, from the visible to the infrared. We show that the absorbed laser energy is localized in an increasingly smaller number of particles with increasing the laser wavelength from 355 nm to 1900 nm. The size of the photomodified regions can be as small as 20 nm. The observed modification is explained by optically induced sintering (coalescence) of colloidal nanoparticles.; In Chapter 4, macroscopic natural optical activity observed in a metal cluster medium is reported. Circular dichroism spectroscopy is performed on a number of different colloidal solutions of silver. Circular dichroism is observed in both monomer and aggregated cluster media. A hypothesis explaining optical activity based on the anomalous crystal structure of the clusters is proposed and discussed.