Figure 7.

(a) g_ext of oval nanohole arrays depends on the shape factor c; presented results are for Ag–NHA at θ = 20°. The best fit to the experimental data is obtained with c = 0.02 (dashed lines are the inversion of g_ext with θ =  − 20°). (b) Absorption density for strongly oval shape (c = 0.1), excited at 903 nm and θ = 20° strongly depends on the excitation handedness. (c) Adding Au on the top of Ag red-shifts the resonances: the total thickness is 55 nm, while legend presents Ag to Au thickness ratio. (d) g_ext spectral position is defined by the grating nature of the NHA; at a single angle of incidence θ = 20°, increasing the starting interparticle distance red shifts the g_ext peak.