Abstract
We present measurements of iso-frequency dispersion surfaces of light scattered from metallic micro-gratings with different periods. The dispersion surfaces, obtained using an infinity-corrected microscope objective, exhibit maxima attributed to diffracted orders as they become evanescent and pronounced minima due to the resonant excitation of surface plasmon polaritons (SPPs). We have also measured the enhanced photoluminescence of a thin layer of dye molecules on top of the grating. This enhanced luminescence is attributed to the local field enhancement close to the surface due to the coupling of the excitation frequency to SPPs. Moreover, we obtain a directional emission of the luminescence, which is attributed to the grating-assisted coupling of SPPs excited by the dye to free space light. The technique used for the measurements presented in this paper can be extended to characterize the angular emission patterns of emitters coupled to micro- and nano-plasmonic structures.
Highlights
2π/a the reflection at positions of larger momentum than the Rayleigh anomalies, corresponding to the resonant excitation of surface plasmon polaritons (SPPs)
Using an infinity-corrected microscope objective, we have investigated the scattering of light from Au micro-gratings with different periods
We have measured the isofrequency dispersion surfaces at λ = 690 nm. These surfaces exhibit maxima attributed to diffracted orders as they become evanescent and minima due to the coupling to SPPs
Summary
The iso-frequency dispersion surface measurements presented can be understood by first having a look at the dispersion relation of light scattered from a grating. The dispersion relation of light scattered from the grating when the incident k-vector is in the plane containing the reciprocal lattice vector and the surface normal (x–z-plane) is schematically represented in figure 1. By patterning a metallic surface with a grating it is possible to couple these SPPs back to free space light with a wave vector given by the relation kout = ±kSPP ± mG. This phenomenon leads to the grating-assisted directional emission from emitters in the proximity of metals [17, 18]
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