Coupled surface plasmons on thin silver gratings

A thin metal film with corrugations on both surfaces is shown to couple visible photons to both the long range surface plasmon polariton (LRSPP) and the short range surface plasmon polariton (SRSPP). It is found that the first harmonic component of the grating shape causes a significant band gap (an anti-crossing) where the LRSPP and the SRSPP should cross. Experimental data are compared with model calculations using a multilayer, multishape differential grating theory. In addition, to clarify the nature of the modes, the time averaged magnetic field distributions and instantaneous electric field profiles are explored, specifically at the anti-crossings of the first-order modes.