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

Realistische Modellierung der NIR/VIS/UV- optischen Konstanten dünner optischer Schichten im Rahmen des Oszillatormodells

Based on a multioscillator approach, we demonstrate the determination of optical constants of different optical coating materials. The advanced LCalc-software allows calculating the dielectric function as well as refractive index and extinction coefficient through a fit of transmittance and reflectance spectra measured at one or several angles of incidence. Sufficiently accurate spectrophotometric measurements are carried out by means of self-developed VN-The thus obtained optical constants are automatically Kramers-Kronig-consistent and in reasonable correspondence to various kind of side information available about the coatings. This is demonstrated for dielectric oxide coatings as well as for one transparent conductive oxide (ITO) and a metal layer (aluminium). In application to reproducibility experiments, the method allows estimating process-inherent stochastic variations in optical constants, which represent themselves an essential input for advanced computational manufacturing runs for design optimization prior to deposition

A hybrid algorithm for reengineering the refractive index profile for inhomogeneous coatings from optical in-situ broadband monitoring data

Reengineering the refractive index profile of inhomogeneous coatings is a troublesome task. Multiplicity of solutions may significantly reduced by providing additional information. For this reason an in-situ broadband monitoring system was developed to measure the transmittance of the growing film directly at the rotating substrate. For characterization of these coatings a new model was developed, which significantly reduces the number of parameters. The refractive index profile may be described by a proper number of equally spaced volume fraction values using the Bruggeman effective media approach. A good initial approximation of the refractive index profile can be generated based an deposition rates for both materials recorded with quartz crystals monitor during manufacturing. During the optimisation process, a second order minimization algorithm was used to vary the refractive index profile of the whole coating and film thickness of the intermediate stages. Finally, a significantly improved accuracy of the modelled transmittance was achieve

Computational manufacturing of optical interference coatings: Method, simulation results, and comparison with experiment

Virtual deposition runs have been performed to estimate the production yield of selected oxide optical interference coatings when plasma ion-assisted deposition with an advanced plasma source is applied. Thereby, deposition of each layer can be terminated either by broadband optical monitoring or quartz crystal monitoring. Numerous deposition runs of single-layer coatings have been performed to investigate the reproducibility of coating properties and to quantify deposition errors for the simulation. Variations of the following parameters are considered in the simulation: refractive index, extinction coefficient, and film thickness. The refractive index and the extinction coefficient are simulated in terms of the oscillator model. The parameters are varied using an apodized normal distribution with known mean value and standard deviation. Simulation of variations in the film thickness is performed specific to the selected monitoring strategy. Several deposition runs of the selected oxide interference coatings have been performed to verify the simulation results by experimental data

Infrared optical constants determination by advanced FTIR techniques

An approach for determining optical constants of uncoated substrates and single layer coatings in the near and mid-infrared spectral regions has been evaluated. Results for different samples are presented and compared with literature data

In situ optical characterization and reengineering of interference coatings

A new optical monitoring system has been developed that allows recording of transmission spectra in the wavelength range between 400 and 920 nm of a growing optical coating during deposition. Several kinds of thin film sample have been prepared by use of a hybrid monitoring strategy that is essentially based on a combination of quartz monitoring and in situ transmission spectra measurements. We demonstrate and discuss the applicability of our system for reengineering procedures of high-low stacks and measurements of small vacuum or thermal shifts of optical coatings

High-reflective coatings for ground and space based applications

High-reflective coatings are indispensable in order to manufacture mirrors with highest possible reflectivity. The maximum reflectivity can be achieved by all-dielectric coatings; however, the spectral bandwidth of these mirrors is limited. For astronomical applications metal based coatings (Al, Au, Ag) are commonly applied, as they allow high reflectivity and at the same time a broad spectral bandwidth

Optical and mechanical properties of oxide UV coatings, prepared by PVD techniques

The present study deals with the characterization of hafnia, alumina, and zirconia coatings as well as mixtures thereof with respect to applications in the UV. Emphasis is placed on optical properties, particularly on the relation between UV refractive index and absorption edge. The shift of the coatings is investigated as well as the mechanical stress. Finally, we present the results of stress measurements performed for quarterwave stacks deposited on different substrates in a broad range of deposition temperatures. In this study, no systematic dependence of the result of the stress measurement on the substrate material and geometry could be identified