Identity of long-range surface plasmons along asymmetric structures and their potential for refractometric sensors

Abstract

The field identity of the long-range surface plasmon (LRSP) mode in an asymmetric metal dielectric structure is elucidated and it is shown that it can be pictured as having a zero crossing of the longitudinal electric field at the middle of the metal film. A parametric dependence between the metal and the dielectric layer thicknesses leading to a LRSP mode in an asymmetric structure is given. The sensitivity of an asymmetric four layer structure supporting a grating excited LRSP mode regarding sensing objectives has been investigated. It is compared with the sensitivity of a usual plasmon mode propagating along a metal–dielectric interface. The existence of an anomalous increase of the reflection coefficient in the case of the LRSP is observed theoretically and experimentally. The comparative study is made on the basis of analytical expressions which reveal that the LRSP does not bring a decisive advantage over the standard plasmon for sensor application but its specific features can be advantageously used once well understood.