Fig. 3

Examples of computed electrical field distributions of the PB modes excited by the RPO beam (the electrical field is given in the normalized values by dividing with the electrical field amplitude of the incident beam at the point 2 nm away from the edge of each nanodisc). a-d PB modes of the 1200 nm Au-nanodisc excited at the incident wavelengths of 0.619 μm, 0.684 μm, 0.8304 μm and 1.291 μm, respectively. e-f PB modes excited at the incident wavelength of 0.619 μm for the 600 nm Au-nanodisc and the 300 nm Au-nanodisc, respectively. As can be determined in Fig. 2(c), all of these wavelengths are slightly larger than the zero phase wavelengths. From (a)-(f), the arrows are plotted with the relative length scale of 1:1:1:1.5:1:0.5 (the smaller scale means that the same length represents smaller electrical field amplitude)