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We study the optical properties of nanostructured self-affine thin films. We use the coupled-dipole equations to describe the interaction of the external electromagnetic wave with nanoparticles. We find that the particle size dispersion can be invoked to tailor the spectrum of local field enhancement and optical dichroism. We also propose self-affine thin films of vanadium dioxide (VO 2 ) as temperature-tunable dichroic devices.

We show that fractal clusters of hollow Si nanoparticles provide both magnetic hotspots (MHs) and electric hotspots (EHs). The hollow size tailors the wavelength dependence of the field enhancement. In the wavelength window 400-750 nm, magnetic field intensity enhancements of 10-3790 and electric field intensity enhancements of 10-400 are achievable. Wavelength-tuned MHs and EHs allow better enhancement of Raman optical activity, fluorescence and circular dichroism of molecules, and so on. Si nanoparticles overcome the limitations of metallic ones, which provide only EHs at the price of heat perturbations on a nearby quantum emitter due to metallic ohmic losses.

We study the optical properties of aggregates of hollow gold nanoparticles: monodisperse and bidisperse random gas particles and fractal cluster-cluster aggregates consisting of 1000 particles. We use the coupled-dipole equations to describe the interaction of the electromagnetic wave with particles. We find that the particle core volume fraction can be tuned to minimize the full width at half-maximum (FWHM) and to considerably shift the peak of the absorption spectrum. We find that the redshift, but not the FWHM of the peak, has a monotonic dependence on the particle core volume fraction. High pass, low pass and band rejection filters can be realized with random and fractal aggregates of hollow particles. In the case of fractal clusters, particle size dispersion has a deep influence on the overall shape of the spectrum. Thus, the aggregates of hollow nanoparticles are superior to the aggregates of solid nanoparticles: their absorption spectrum can be easily engineered by hollow size.