Figure 4: Measured absorptivity versus incidence angle.
The absorptivity spectrum is obtained as A(λ)=1–R(λ)–T(λ), where A(λ) is the spectral absorptivity, R(λ) the reflectivity of the metamaterial, and T(λ) is the transmissivity, which is negligible for the metamaterial with four periods. The measured absorptivity is in complete agreement with the theoretically predicted absorptivity presented in Fig. 3. Only reflectivity measurements are needed as we use a 100 nm thick tungsten substrate underneath the metamaterial which is intransparent over the measured wavelength range. The inset shows measured absorptivity of the tungsten/hafnium dioxide metamaterial at a 13o angle of incidence from 0.5 to 10 μm. The observed long-wavelength absorptivity characteristics are in complete agreement with the effective medium calculation.
