In metal optics gold assumes a special status because of its practical importance in opto-electronic and nano-optical devices, and its role as a model system for the study of the elementary electronic excitations that underlie the interaction of electromagnetic fields with metals. However, largely inconsistent values for the frequency dependence of the dielectric function describing the optical response of gold are found in the literature [1][2][3]. We performed precise spectroscopic ellipsometry measurements on evaporated gold, template-stripped gold, and single-crystal gold to determine the optical dielectric function across a broad spectral range of 300 nm -25 µm (0.05 -4.14 eV) with high spectral resolution. We fit the data to the Drude free-electron model, with an electron relaxation time τD = 14 ± 3 fs and plasma energy ωp = 8.48 eV. We find that the variation in dielectric functions for the different types of samples is small compared to the range of values reported in the literature. Our values, however, are comparable to the aggregate mean of the collection of previous measurements from over the past six decades. This suggests that although some variation can be attributed to surface morphology, the past measurements using different approaches seem to have been plagued more by systematic errors than previously assumed.

All-dielectric metamaterials offer a potential low-loss alternative to plasmonic metamaterials at optical frequencies. Here, we take advantage of the low absorption loss as well as the simple unit cell geometry to demonstrate large-scale (centimeter-sized) all-dielectric metamaterial perfect reflectors made from silicon cylinder resonators. These perfect reflectors, operating in the telecommunications band, were fabricated using self-assembly based nanosphere lithography. In spite of the disorder originating from the self-assembly process, the average reflectance of the metamaterial perfect reflectors is 99.7% at 1530 nm, surpassing the reflectance of metallic mirrors. Moreover, the spectral separation of the electric and magnetic resonances can be chosen to achieve the required reflection bandwidth while maintaining a high tolerance to disorder. The scalability of this design could lead to new avenues of manipulating light for low-loss and large-area photonic applications.

All-dielectric metamaterials utilizing Mie resonances in high-permittivity dielectric resonators offer a low-loss alternative to plasmonic metamaterials. Here we present the demonstration of a single-negative all-dielectric metamaterial, comprised of a single layer of cylindrical silicon resonators on a silicon-on-insulator substrate, that possesses peak reflectance over 99% and an average reflectance over 98% across a 200 nm wide bandwidth in the short-wavelength infrared region. The study is also extended to disordered metamaterials, demonstrating a correlation between the degree of disorder and the reduction in reflectance. It is shown that near-unity reflection is preserved as long as resonator interaction is avoided. Realization of near-unity reflection from disordered metamaterials opens the door to large-area implementations using low-cost self-assembly based fabrication techniques.

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We present an effective-medium model for calculating the frequency-dependent effective permittivity (ω) and permeability µ(ω) of metamaterial composites containing spherical particles with arbitrary permittivity and permeability. The model is derived from the zero-scattering condition within the dipole approximation, but does not invoke any additional long-wavelength approximations. As a result, it captures the effects of spatial dispersion and predicts a finite effective refractive index and antiresonances in (ω) and µ(ω), in agreement with numerical finite-element calculations.