Jari Lindberg

Mathematical concepts of optical superresolution

Optical imaging beyond the diffraction limit, i.e., optical superresolution, has been studied extensively in various contexts. This paper presents an overview of some mathematical concepts relevant to superresolution in linear optical systems. Properties of bandlimited functions are surveyed and are related to both instrumental and computational aspects of superresolution. The phenomenon of superoscillation and its relation to superresolution are discussed.

Spectral analysis of resonant transmission of light through a single sub-wavelength slit

We analyze the spectral properties of resonant transmission of light through a sub-wavelength slit in a metal film. We show that the enhanced transmission can be understood in terms of interfering surface-wave-like modes propagating in the slit. We characterize the effect of geometrical and material properties of the slit on the transmission spectrum. Furthermore, we show that the wavelength of the transmission resonance strongly depends on the surrounding medium. This effect may be utilized in sensors, imaging, and the detection of, e.g. biomolecules.

Spatial coherence effects in light scattering from metallic nanocylinders

We study the scattering of a partially coherent electromagnetic beam from metallic nanocylinders and analyze the effects of plasmon resonances on the coherence and polarization properties of the optical near field. We employ the coherent-mode representation for the incident field and solve the scattering problem independently for each mode by using a boundary-integral method. Our results show that the plasmon resonances may significantly affect the coherence and polarization characteristics of the near field and that partial coherence influences the energy flow in nanocylinder arrays.

Rotational frequency shifts in partially coherent optical fields

We study the frequency shifts taking place when a random, stationary optical field rotates with respect to an observer. The field is expanded in terms of fully coherent Laguerre-Gaussian basis modes, for which the rotational frequency shifts have been studied previously. We demonstrate the formalism by considering the spectrum of a Gaussian Schell-model field, and show that for a spatially highly incoherent field, significant spectral changes can be expected.

Dipole-dipole interaction between molecules mediated by a chain of silver nanoparticles

We study the dipole-dipole coupling between two fluorescent molecules in the presence of a chain of metallic nanoparticles. We analyze the spectral behavior of the coupling strength and its dependence on the molecular orientation. Our results show that for certain resonant wavelengths the coupling strength between the molecules is greatly enhanced and is strongly polarization sensitive. We also demonstrate how metallic nanoparticles can be utilized in implementing a polarization-sensitive coupler.

Degree of polarization in light transmission through a near-field probe

We analyse the changes in the partial polarization of random, stationary light fields in transmission through a near-field probe. The probe is modelled as a two-dimensional metal-coated optical fibre tip through which the field is propagated by applying the boundary-integral method. Both the magnitude of the opening angle and the aperture size of the probe are found to significantly influence the partial polarization of the field. We discuss the results in terms of both the conventional two-dimensional and the recent three-dimensional formalism for the degree of polarization.