Theoretical and experimental studies of metal-infiltrated opals

The optical properties of metal-infiltrated synthetic opals have been studied analytically, numerically, and experimentally in the visible and infrared spectral ranges. A simple model of weakly interacting resonant cavities is proposed to qualitatively understand the dispersion of electromagnetic waves in metallic photonic crystals. In the approximation of an ideal metal infiltrated into opals this model is exact, and the frequencies of the propagating modes in metallic opals are close to the eigenfrequencies of a single spherical resonator. Photonic band structures based on the dispersion of a metal dielectric constant have been calculated numerically for several metals and show similarity with the ideal metal model. Reflectivity and transmission spectra of thin-film metallic opals are calculated. Growth and saturation of the reflectivity spectra at low frequencies are manifestations of the omnidirectional band gap. The sharpest minimum in the reflectivity and maximum in the transmission spectra correspond to the position of the cutoff frequency. Silver- and copper-infiltrated opals were fabricated and their reflectivity spectra were measured in the visible to mid-IR spectral range. These spectra are in a good agreement with the theoretical calculations.