RESUMO
Application of electric field and moderately elevated temperature depletes the side facing anode from alkali present in glasses. The change of composition of the treated glass results in variation of refractive index depth profile within the treated glass. Spectroscopic ellipsometry is employed for characterization of optical properties of glass treated in different conditions. The results of optical characterization are verified by secondary ion mass spectroscopy. It is found that the refractive index profile obtained from ellipsometry has a maximum value higher than the one of untreated glass. The obtained refractive index profiles are in very good agreement with concentration profiles.
RESUMO
Metal-dielectric phase-shifting multilayer optical elements have been developed, providing broadband, virtually dispersion-free polarization manipulation down to the few-cycle level. These optical elements are Ag/Al2O3 mirrors that operate in the spectral range from 500 to 100 nm, exhibiting reflectance higher than 95%, and a differential phase shift between the s- and p-polarization of about 90° distributed over four bounces. The mirrors have been designed, produced, and reliably characterized based on spectral photometric and ellipsometric data using a non-parametric approach as well as a multi-oscillator model. The optical elements were implemented into a few-cycle laser system, where they transformed linearly polarized few-cycle light pulses to circular polarization.
RESUMO
The anti-reflective effect of dielectric coatings used in silicon solar cells has traditionally been the subject of intensive studies and practical applications. In recent years the interest has permanently grown in plasmonic layers based on metal nanoparticles, which are shown to increase light trapping in the underlying silicon. In the present work we have combined these two concepts by means of in situ synthesis of Au nanoparticles in a dielectric matrix (TiO2), which is commonly used as an anti-reflective coating in silicon solar cells, and added the third element: a 10-20% porosity in the matrix. The porosity is formed by means of a controllable wet etching by low concentration HF. As a consequence, the experimentally measured reflectance of silicon coated by such a plasmonic layer decreases to practically zero in a broad wavelength region around the localized surface plasmon resonance. Furthermore, we demonstrate that extinction and reflectance spectra of silicon coated by the plasmonic films can be successfully accounted for by means of Fresnel formulae, in which a double refractive index of the metal-dielectric material is used. This double refractive index cannot be explained by effective medium theory (Maxwell-Garnett, for example) and appears when the contribution of Au nanoparticles located at the TiO2/Si interface is high enough to result in formation of interface surface plasmon modes.
RESUMO
The width of the surface plasmon resonance of metallic particles increases as the particle size reduces due to confinement effects that modify the metal dielectric function. In the limit of very low particle concentration, particle size can be directly related to the plasmon width. However, as concentration increases, the interaction among particles induces additional broadening. Numerical computation of the effective dielectric function of systems consisting of monodisperse and randomly distributed particles embedded in a dielectric matrix enable us to quantify the influence of both size and interaction effects. It is shown that for noble metals the contribution of interparticle interaction to plasmon resonance width cannot be neglected even at volume concentrations of a few per cent. The results presented here can be useful in extending nanoparticle sizing from optical extinction spectroscopy beyond the dilute limit required by classical Mie theory.