RESUMEN
HfO2/SiO2 periodic multilayer high reflection mirrors have been prepared by a reactive electron-beam evaporation technique. The deposited mirrors were annealed in the temperature range from 300°C to 500°C. The effects of annealing on optical, microstructural, and laser-induced damage characteristics of the mirrors have been investigated. The high reflection band of the mirror shifts toward a shorter wavelength with increasing annealing temperature. As-deposited and annealed mirrors show polycrystalline structure with a monoclinic phase of HfO2. Crystalinity and grain size increase upon annealing. The laser-induced damage threshold (LIDT) has been assessed using a 532 nm pulsed laser at a pulse width of 7 ns. The LIDT value of the multilayer mirror increases from 44.1 J/cm2 to 77.6 J/cm2 with annealing up to 400°C. The improvement of LIDT with annealing is explained through oxygen vacancy defects as well as grain-size-dependent thermal conductivity. Finally, the observed laser damage morphology, such as circular scalds and ablated multilayer stacks with terrace structure, are analyzed.
RESUMEN
HfO(2)-SiO(2) mixed composite thin films have been deposited on fused silica substrate by co-evaporation of HfO(2) and SiO(2) through the reactive electron-beam evaporation technique. The composition-dependent refractive index and the absorption coefficient have been analyzed using different effective medium approximation (EMA) models in order to evaluate the suitability of these models for such mixed composite thin films. The discrepancies between experimentally determined and EMA-computed values are explained through microstructural and morphological evolutions observed in these mixed composite films. Finally, the dependence of the laser damage threshold as a function of silica content has been investigated, and the improved laser-induced damage threshold for films having more than 80% silica content has been explained through the defect-assisted multiphoton ionization process.
RESUMEN
Post nondestructive analyses of an all-dielectric multilayer Fabry-Perot interference filter developed through a reactive electron beam deposition process have been carried out through numerical reverse engineering of transmission spectra, Rutherford backscattering spectroscopy and quartz crystal monitoring data to derive multilayer geometry, deposited layer thicknesses, densities, refractive indices, compositions, and stoichiometry. These techniques are collectively used to fulfill the missing links with complementary and some supplementary information to inverse synthesize the multilayer geometry. During this investigation it is distinctly understood that the factors associated with real-time deposition have significantly influenced the microscopic parameters, namely, the densities and refractive indices of TiO2 and SiO2 layers. This in turn influenced the layers' geometric (physical) thicknesses during automated quarter-wave optical layer monitoring and consequently affected the experimental spectral characteristics. The role of oxygen has been observed to be significant in controlling the mass densities of these refractory oxide layers. It is further noticed that the layer density values have been significantly perturbed whether the associated TiO2 or SiO2 oxide dielectric films are substoichiometric (oxygen-deficient), stoichiometric, or superstoichiometric (oxygen-enriched).
RESUMEN
Codeposited gadolinia silica composite films have been probed for their growth-dependent optical and microstructural properties using phase-modulated spectroscopic ellipsometry and scanning probe microscopy. The mean refractive indices were computed using an effective ellipsometric multilayer modeling approach. Most of the composite films have shown growth-induced nonlinear refractive indices to some extent. However, the mean optical properties have depicted interesting trends in the microstructural evolutions. Gadolinia silica composite films in the composition ratio ranging from 90:10 to 70:30 have depicted superior optical as well as morphological properties. Unlike conventional oxide films, these composite films displayed microstructural, spectral refractive index, and bandgap supremacy over the pure films. Such an observation cannot be explained by the empirical Moss law. Atomic force microscopy also revealed a superior morphology in the composite films. The autocorrelation and height-height correlation functional analysis have distinctly supported such superior microstructural features in the composite films, which justifies the supremacy of the optical properties. Such an observation has opened up possibilities to utilize such composite films toward deep-and extreme-ultraviolet spectral regions of the electromagnetic spectrum.