Heat assisted magnetic recording (HAMR) requires a sufficiently small heat spot, which is much below the diffraction
limit of the wavelength of the used light. This can be achieved with an optical near field source consisting of a small
metallic wedge which supports edge plasmons. The power transfer between a dielectric rectangular waveguide and this
metallic wedge is investigated in simulations and experiments. Beating of two eigenmodes of this system leads to power
oscillations between the waveguide core and the edge plasmon along their overlap length. This was confirmed in near
field experiments which are based on the evaporation of phase change material with the absorbed optical near fields as
heat source. Devices with weak and strong edge plasmon excitation could be clearly distinguished in a simple far field
experiment.
We investigate light concentration and field enhancement in nanometer-scale ridged aperture antennae. Resent numerical simulations have shown that nanoscale ridged apertures can concentrate light into nanometer domain. Most importantly, these ridge apertures also provide an optical transmission enhancement several orders of magnitude higher compared to regularly shaped nanoscale apertures. We employ the finite-difference time-domain (FDTD) method to design these apertures and fabricate them in thin metal films. A home-built near field scanning optical microscope (NSOM) is used to map the near-field intensity distribution of the light transmitted through these apertures. It is shown that the ridged apertures can produce a concentrated light spot far beyond the diffraction limit, with transmission enhancement orders of magnitude higher than regularly shaped apertures. Nanolithography applications of these nanoscale ridged aperture antennae are demonstrated.
The optical transmission mechanism through a ridge nano-aperture in a metal film is discussed based on the waveguide theory and FDTD computations. The transmission enhancement through ridge apertures is associated with the TE10 waveguide propagation mode. In terms of near and far field radiator, the ridge aperture can be represented as a combination of an oscillating electric dipole and two magnetic dipoles. The effects of localized surface plasmon (LSP) excited on the edges of ridge nano-apertures made in silver are discussed. The transmission enhancement and field concentration functions of ridge apertures are confirmed by contact lithography experiments.
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