We develop a method to detect surface plasmon polaritons (SPP) launched by a sub-wavelength slit structure
using optical microscopy. The mechanism relies on an ultra-thin layer of polymer, whose thickness is varied with
nano-scale precision to enable matching between the momentum of incident light and that of SPPs on the metal
surface adjacent to the slit exit. At an optimal layer thickness, the SPP coupling efficiency is enhanced about
six times relative to that without the layer. The enhanced efficiency results in distinctive and bright signatures
visible under a far-field optical microscope. We show how this method can be used for parallel measurement of
SPPs through a simple experiment in which the SPP propagation distance is extracted from a single microscope
image. We also use optical microscopy to image SPPs focussed by a curved array of holes, obtaining results that
are consistent with previous measurements using near-field optical microscopy.
We propose a high efficiency coupling scheme of surface plasmon polaritons (SPP) in a metal-dielectric slit structure. The design includes a narrrow silver-slit structure, which is immersed in a dielectric with refractive index 1.5. We map the dependence of SPP coupling efficiency on the dielectric layer thickness (d). By varying d the dispersion behavior of the SPP mode is tuned enabling minimized wavevector mismatch between the light exiting the slit and the SPP mode. A dielectric layer of thickness in the range 50 nm < d < 150 nm yields coupling efficiencies of approximately 80%, representing a nearly four-fold enhancement relative to the coupling efficiency without a dielectric layer.