Magnetoplasmonic nanostructures

Surfaces that are nanopatterned, metallic, and magnetic can support surface plasmon resonances, providing an alternative and effective way to reconfigure flat optical components. Utilising a range of near- and far-field characterisation techniques, the optical and magneto-optical properties of lithographically patterned thin magnetic films are investigated. A magneto-optical diffractometer was designed, assembled, and commissioned to characterise periodic magneto-plasmonic nanostructures. For Ni and Co nanostructured antidot arrays, enhanced values of the magneto-optical Kerr rotation were recorded for energies and angles corresponding to excitations of surface plasmon polaritons. This enhancement was found to be thickness dependent. Modification of the optical properties via applied transverse magnetic fields and the excitation of surface plasmon polaritons, was demonstrated for an antidot array of pure Ni. The excitation was also shown to enhance the generation of second harmonics, as well as further activate nonlinear-optical mechanisms. In order to fully resolve and explain the source of this remarkable magneto-optical activity, near field probing techniques were used. This allows for mapping the electric near-field with a sub-wavelength resolution, thereby revealing the interplay between the light and the nanostructured lattice. The measurements show that the electric near field intensification, induced by plasmon excitation, increases the polarisation conversion, which correlates to the observed magneto-optical Kerr rotation