Comment on “Enhanced transmission of light through a gold film due to excitation of standing surface-plasmon Bloch waves”

The purpose of this Comment is first to correct the claim of Smolyaninov and Hung [Phys. Rev. B 75, 033411 (2007)] that the reported results “strongly contradict” the presence of diffracted evanescent waves in the vicinity of subwavelength structures and second to point out that periodic structures are unnecessary for the efficient production of the surface plasmon polariton guided mode either as traveling or standing waves. Guided surface waves originate from simple slit or groove edges illuminated under normal incidence, and one-dimensional surface cavities from these standing waves are easily realized.

Figure 1

(Color online) FDTD calculation of $E_z$ amplitude as a function of $z$ (perpendicular distance from the slit-groove reference plane) and $y$ (transverse distance along the slit-groove reference plane). The center-to-center distance between the slit and groove is $3.6\mu \mathrm{m}$. Slit and groove are both milled $100\mathrm{nm}$ wide; the groove depth is $100\mathrm{nm}$, and the silver layer is $400\mathrm{nm}$ thick. The incident light has a free-space wavelength ${\lambda }_0=852\mathrm{nm}$. This plot is an unpublished result from Xie and Mansuripur, shown here with permission.

Figure 2

(Color online) FDTD calculations of $H_x$ amplitude as a function of $z$ and $y$ for the same structures as in Fig. 1. The $H_x$ component of the magnetic field is aligned with the long axes of the slit and groove. This plot is an unpublished result from Xie and Mansuripur, shown here with permission.