Current Research Topic: Nano-photonics near interfaces

The Theoretical Optics Group is investigating energy flow patterns in electromagnetic radiation fields on a sub-wavelength scale. Of particular interest is the radiation emitted by a small localized source, like an atom, molecule or nanoparticle, near an interface with a material medium. We have been able to predict the existence of singularities and vortices in the flow line patterns, and we are studying these spatial structures with sub-wavelength (nanoscale) precision. Recently we found that radiation emitted by a linear electric dipole near an interface has a four-vortex structure near the particle. In free space, the energy is emitted along straight lines, but as a result of interference between the emitted radiation and its own reflection at the interface, the emission exhibits an intricate vortex pattern.

When the radiating particle is embedded in an absorbing medium, the mechanism of energy emission alters dramatically, as compared to the emission in free space. We have found that the surrounding material does not only weaken the energy flow, but that there is also a spatial redistribution of the energy flow. The field lines of energy flow for a linear dipole become curves, and some of these curves return to the location of the particle. Energy emitted along these field lines is non-radiative, since the energy flows back to the source rather than to the far field.

Metamaterials are artificially structured composites which may have a negative permittivity, a negative permeability, or both. When both the permittivity and the permeability are negative, the index of refraction is also negative. Reflection and refraction of light at the interface with a medium with a negative index of refraction appears to defy the known laws of physics. In particular, when radiation from a small particle passes through a slab of material with a negative index of refraction, it may come to a focus at the other side. It has been speculated that this may clear the way to the construction of a superlens, which can form an image of an object with a precision less than an optical wavelength. We are investigating the energy propagation through such metamaterials with nanoscale resolution.