Enhanced Directed Radiative Surface Plasmon Emission from Periodically Corrugated Noble Metal Films

Massively enhanced directed radiation emission from periodically corrugated thin gold and silver films at the surface plasmon resonance is reported. The optical setup comprises attenuated total reflection in a modified Kretschmann configuration, with the semi-transparent metal films placed at the base plate of a polymeric semi-cylinder. Experiments performed at a fixed wavelength confirm earlier observations on appearance of two symmetrically arranged first-order diffraction beams. These emanate under resonance conditions into the upper and lower half-spaces, the latter due to coupling of the non-radiating surface plasmon to an angularly directed radiative mode. Collimated incident and spectrally broadband radiation under resonance conditions likewise split into two symmetrically arranged first-order, but spectrally dispersed continuous, diffraction beams. For silver, unlike smooth metal films, the non-radiative surface plasmon (SP) also splits into two spectrally separated resonance dips at 550 and 700 nm. The spectral continuum in the SP-mediated radiative beam in the lower half-space resembles the complementary color feature of the absorbing SP-mode. Its intensity exceeds the isotropic radiative plasmon emission from smooth, weakly roughened SP-active gold metal layers by at least two orders of magnitude.