Deposition and spectral performance of an inhomogeneous broadband wide-angular antireflective coating

The gradient index coatings and optical filters based on them are a challenge for fabrication. In a round-robin experiment basically the same hybrid antireflection coating for the visible spectral region has been deposited with three different techniques: electron beam evaporation, ion beam sputtering and radio frequency magnetron-sputtering. Spectral performances of such one-side and both-side coated samples have been compared with corresponding theoretical spectra of the designed profile. Also, reproducibility of each process is checked

Evolution of grain boundary network topology in 316L austenitic stainless steel during powder hot isostatic pressing

The grain boundary network evolution of 316L austenitic steel powder during its densification by hot isostatic pressing (HIPing) was investigated. While the as-received powder contained a network of random high angle grain boundaries, the fully consolidated specimen had a large fraction of annealing twins, indicating that during densification, the microstructure evolves via recrystallization. By interrupting the HIPing process at different points in time, microstructural changes were tracked quantitatively at every stage using twin boundary fractions, distribution of different types of triple junctions, and the parameters associated with twin related domains (TRDs). Results revealed that, with increase in temperature, (i) the fraction of annealing twins increased steadily, but they mostly were not part of the grain boundary network in the fully consolidated specimen and (ii) the average number of grains within a TRD, the length of longest chain, and twinning polysynthetism increased during HIPing and (iii) the powder characteristics and the HIPing parameters have a strong influence on the development of grain boundary network. Based on the results obtained, possible alterations to the HIPing process are discussed, which could potentially allow twin induced grain boundary engineering

In situ and ex situ spectrophotometric characterization of single- and multilayer-coatings I: Basics

Optical spectrophotometry provides a powerful tool for the characterization of modern coatings, no matter whether they are manufactured for optical or non-optical applications. Spectrophotometry of coatings gives primary access to optical constants and their dispersion as well as to the film thickness. In a second step, the application of sophisticated KramersâKronig-consistent dispersion models gives further access to related quantities, including density, porosity, but also charge carrier density, crystalline structure, band structure and possible impurities of the coating. We will present and discuss the state of the art in spectrophotometry of single and multilayer coatings, including their in situ as well as ex situ versions. In situ spectrophotometry allows re-engineering as well as monitoring the deposition process of a growing coating, resulting in excellent specification adherence particularly in the field of optical coatings

Theoretical study of multilayer coating reflection taking into account third-order optical nonlinearities

A theoretical approach is presented that allows calculating the reflectance of dielectric multilayer coatings taking third-order optical nonlinearities into account. The description is based on third-order optical susceptibility so that nonlinear refraction and two-photon absorption processes are automatically considered in terms of the real and imaginary parts of the susceptibility. Two model systems are calculated in order to demonstrate the physical validity of the approach: a mirror that is optimized for maximum reflectance at a given wavelength and a given incident intensity and a mirror that provides a rather flat dependence of the reflected intensity on the incident one. Model calculations are performed for laser wavelength values of 1064 nm, 800 nm, and 532 nm

Beta-distributed oscillator model as an empirical extension to the Lorentzian oscillator model: Physical interpretation of the β do model parameters

The physical sense of the free parameters of the beta-distributed oscillator (β do) dispersion model is discussed. It is shown that the set of six model parameters provides information on central wavenumber, oscillator strength, absorption edge position, asymmetry, as well as homogeneous and inhomogeneous linewidth of a complicated absorption feature. For materials satisfying the Moss rule, the number of independent β do parameters decreases down to five. We also show that the Cody absorption edge shape essentially represents a special case of the β do approach. By making use of the generalized Miller rule, we propose a generalization of the β do model to nonlinear refractive indices and absorption coefficients