Interaction of nanostructures with deterministic and stochastic electromagnetic fields

Commonly, the optical response of a nanostructure is obtained by using plane-wave excitation. However, a different form of optical excitation may modify the response of the nanostructure. I present a theoretical study of the response of a spherical semiconductor quantum dot upon two different excitation forms: (1) a highly confined optical field and (2) an azimuthally polarized laser beam. Highly confined optical fields are encountered in high-resolution nearfield microscopy, and inhomogeneous laser beams, such as an azimuthally polarized beam, are used in confocal microscopy. I find that for these excitation forms, high-order multipole terms are needed to describe the optical response of the quantum dot. I derive the selection rules and the absorption rate corresponding to the contribution of the electric quadruple and the magnetic dipole. For a highly confined field, probing electric quadrupole transitions yields no-improvement of the spatial resolution compared to the resolution obtained by probing electric dipole transitions. For an azimuthally polarized laser beam, the detection of the ratio of the electric dipole and magnetic dipole absorption rates enhances the spatial resolution which is limited by the purity of the modes of the laser beam.; In recent experiments it was observed that the damping of an oscillator increases as it is brought close to the surface of a material. To address this problem, I calculate the damping of a classical oscillator induced by the electromagnetic field generated by thermally fluctuating currents in the environment. The fluctuation-dissipation theorem is applied to derive the linear-velocity damping coefficient. The theory is applied to a particle oscillating parallel to a flat substrate and numerical values for the damping coefficient are evaluated for particle and substrate materials made of silver and glass. I find that losses are much higher for dielectric materials than for metals because of the higher resistivity. I predict that measurements performed on metal films are strongly affected by the underlying dielectric substrate and I show that the theory reproduces existing theoretical results in the non-retarded limit. The theory provides an explanation for the observed distance-dependent damping in shear-force microscopy. The theory should be of importance for the design of nanoscale mechanical systems and for understanding the trade-offs of miniaturization.