Fig. 5: Anisotropic bright–dark contrast in Au disks with various diameters on LiNbO₃.

a, b \({{S}}_{{\mathrm{bright}}}/{{S}}_{{\mathrm{dark}}}\) at two orthogonal sample orientations for gold disks on LiNbO₃, respectively. The green arrows in a and b indicate the \({{\omega }}_{{\mathrm{TO}}{i}}\) along b- and c-axes, respectively. The diameters of the disks are 1 μm, 3 μm, and 5 μm. \(\left|{1}/{{\beta }}_{{b}}\right|\) is plotted in a. \(|{1}/{{\beta }}_{{\mathrm{eff}}}|\) with \({{\varepsilon }}_{{\mathrm{eff}}}=\sqrt{{{\varepsilon }}_{{b}}{{\varepsilon }}_{{c}}}\) is plotted in b. Inset of a shows a photo of the LiNbO₃ wafer. Note there are no corner cuts to help identify the c-axis. The electric field is set to be parallel to the edges of the LiNbO₃. The scale bar is 10 mm. c, d \({{\phi }}_{{\mathrm{bright}}}-{{\phi }}_{{\mathrm{dark}}}\) for the same disks under the same sample orientation with a and b, respectively. Yellow arrows in c and d indicate the \({{\omega }}_{{\mathrm{LO}}{i}}\) along b- and c-axes, respectively. \({1}/{{\beta }}_{{b}}\) and \({1}/{{\beta }}_{{\mathrm{eff}}}\) phases are shown in solid curves in c and d, respectively.