How Holes Can Obscure the View: Suppressed Transmission through an Ultrathin Metal Film by a Subwavelength Hole Array

If a metal film, thick enough to be totally opaque, is perforated by tiny subwavelength holes in an orderly fashion, the transmission will be enhanced extraordinarily [T. W. Ebbesen, et al. Nature (London) 391, 667 (1998)]. Here, we investigate the transmission through an ultrathin semitransparent Au film with a square array of subwavelength holes and observe the opposite behavior: less light is transmitted through the pierced metal compared to the closed film.

Figure 1

Scanning electron microscope image and scheme of the investigated hole array. Parameters: period $P=300\mathrm{nm}$; hole diameter $d=200\mathrm{nm}$; Au film thickness $t=20\mathrm{nm}$. The light is polarized with the plane of incidence ($p$ polarization); the angle of incidence is denoted by $\theta$, the azimuth angle by $\alpha$.

Figure 2

Transmission spectra of (a) the pristine Au film and (b) the hole array at normal incidence. The transmission through the array can be perfectly fitted by using slightly modified Au dielectric constants and one additional Lorentz oscillator. The dashed line in panel (a) corresponds to the transmission calculated for a closed metal film with dielectric properties identical to the Au of the perforated film.

Figure 3

Transmission spectra of the hole array measured for varying angles of incidence $\theta$ with $p$ polarization (a) along the holes; (b) under 45°. In both graphs, the curves have been plotted with subsequent vertical offsets of 0.3.

Figure 4

$\overrightarrow{k}$-dependent plasmon energies from Eq. (3) (black lines) and obtained minima from Fig. 3 (red dots). The different branches correspond to different pairs of values ($m$, $n$) as indicated.