Surface Plasmon Polaritons and Their Role in the Enhanced Transmission of Light through Periodic Arrays of Subwavelength Holes in a Metal Film

We present results of the transmitted, reflected, and absorbed power associated with the enhanced transmittance of light through a silver film pierced by a periodic array of subwavelength holes. Comparing experimentally acquired dispersion curves under different polarization conditions shows that the transmission features of the array are consistent with $p$-polarized resonant modes of the structure. By exploring the regime in which no propagating diffracted orders are allowed, we further show that the transmittance maxima are associated with both reflectance minima and absorption maxima. These new results provide strong experimental evidence for transmission based on diffraction, assisted by the enhanced fields associated with surface plasmon polaritons.

Figure 1

Measured transmittance of the silver hole array for unpolarize light. To the left (a) is the normal incidence transmittance spectrum. To the right (b) transmittance is displayed as a function of in-plane wave vector and frequency in the form of a grey-scale dispersion diagram; black is low transmittance, white is high, and the data in (b) are shown on a logarithmic scale [the array period is (a)]. Also shown are the light lines (dotted lines) where diffracted orders become tangent to the surface; the different diffracted orders are indicated according to whether they occur in the substrate (glass) or air. [These light lines can be found by replacing ${\mathbf{k}}_{\mathrm{mode}}$ in Eq. (1) with the value 0.]

Figure 2

Measured transmittance as a function of in-plane wave vector and frequency in the form of a grey-scale dispersion diagram for $p$-polarized incident light (a) and $s$-polarized incident light (b). Also shown are the calculated SPP dispersion curves for planar surfaces. Data are shown on a linear scale and dark regions are the primary indication of coupling to modes. The arrows indicate the offset between the experimentally derived and the theoretically predicted mode dispersions.

Figure 3

Measured reflectance as a function of in-plane wave vector and frequency in the form of a grey-scale dispersion diagram for $p$-polarized incident light incident from the air side (a) and the glass side (b). Also shown are the relevant calculated SPP dispersion curves for planar surfaces. Data are shown on a linear scale. The dark vertical stripes near $k_{\parallel }=0$ are an experimental artifact. Arrows to indicate the offset between the experimentally derived and theoretically predicted mode dispersions have been omitted in this figure.

Figure 4

Transmittance, reflectance, and inferred absorbance spectra for $p$-polarized incident light at in-plane wave vectors of $0.03\mu {\mathrm{m}}^{-1}$ (a) and $0.15\mu {\mathrm{m}}^{-1}$ (b).