Figure 1
From: Ultrahigh-Q metallic nanocavity resonances with externally-amplified intracavity feedback

Schematic of a metallic nanoslit array with resonant SPP and CM excitations.
Coupling of external light with the fundamental CM is described by the single-interface transmission τ and internal reflection ρin coefficients, respectively. SPPs at the entrance and exit interfaces lead to resonant behavior of τ and ρin that drastically modify CM resonance properties inside the slits.