Experimental demonstration of artificial dielectrics with a high index of refraction

Recently, it has been suggested that metamaterials with high refractive index can be constructed using metal gratings with periodic subwavelength slits [J. T. Shen et al., Phys. Rev. Lett 94, 197401 (2005)]. We designed such metamaterials and investigate their transmittance and reflectance in the terahertz frequency range. The spectra can be directly compared to that of a conventional dielectric slab with effective refractive index of $n\simeq 5.5$. As theoretically predicted, the effective index of refraction only depends on the ratio of the width of the slits to the periodicity of the gratings. Existing small differences to the dielectric slab are discussed.

Figure 1

(Color online) Schematic geometry of the transmittance and reflectance experiment. $\vec{k}$, $\tilde{e}$, and $\tilde{h}$ are the wave vector, electric field, and magnetic field of the electromagnetic wave, respectively. The characteristic dimensions of the metallic gratings are $d=0.6\mathrm{mm}$, $a=0.1\mathrm{mm}$, $L=2.01∕1.01\mathrm{mm}$, and the sample cross section is $15\times 15\mathrm{mm}$. The picture shows the grating with $L=2.01\mathrm{mm}$

Figure 2

(Color online) Transmittance (upper panel), phase shift (middle), and reflectance (lower) of the metallic grating shown in Fig. 1. Symbols: experiment, lines: model calculations assuming $L_{\mathrm{eff}}=0.372\mathrm{mm}$ and $n_{\mathrm{eff}}=5.51$. See text for details.

Figure 3

(Color online) Transmittance (upper panel), phase shift (middle), and reflectance (lower) of dielectric slab with $L=0.987\mathrm{mm}$ made from magnesium oxide. Symbols: experiment, lines: model calculations assuming $n\left(\nu \right)=3.11+(0.002+0.0002i)\nu$.