The field of optical coating is as large as the field of optics itself. Virtually every optical surface in every optical instrument benefits from a coating that assures its correct optical properties. In this role optical coating is known as an enabling technology because coatings enable the performance of optical systems. However there are also applications where the optical coating itself plays the leading role by defining the technology. Anticounterfeiting devices, sensitive detectors of miniscule amounts of material, certain display systems, are some examples. The field is huge and beyond even this conference completely to cover. This account, therefore, picks just a few topics mostly of particular interest to the author and follows some of the progress made in them over the years.

A customized planetary rotation stage has been fitted to a commercial ion beam sputter coater to enable the deposition of high uniformity, multilayer optical coatings on large substrates without the use of masks. Uniformity in this system achieved by sequentially depositing each layer in two fixed locations in the sputtered particle plume where the geometry of the natural thickness distributions on a rotating substrate in these locations are of complementary shape and add to produce an overall uniform layer. The modified planetary stage allows substrate rotation about its own axis at any fixed position of the substrate centre about the axis of the planetary system. The suitable locations in the plume of each material that allow maximum uniformity are found by trial and error refinement of locations obtained by modelling of the plume distribution and expected thickness distributions. Ellipsometric monitoring of the thickness of the layer in each fixed position is used to determine the precise ratio of thicknesses in each location needed to obtain the correct total layer thickness simultaneously with high uniformity. The system has thus far enabled single wavelength antireflection coatings of less than 0.001% reflectance to be fabricated over 270 mm diameter substrates. This requires the film thickness uniformity on all layers to be less than ± 0.2%. In addition, 4-layer, dual wavelength antireflection coatings have been fabricated with less than 0.01% reflectance on both wavelengths over similar substrate dimensions.

This paper describes optical, durablility and environmental performance of a germanium carbide based durable antireflection coating. The coating has been demonstrated on germanium and zinc selenide infra-red material however is applicable to other materials such as zinc sulphide. The material is deposited using a novel reactive closed field magnetron sputtering technique, offering significant advantages over conventional evaporation processes for germanium carbide such as plasma enhanced chemical vapour deposition. The sputtering process is "cold", making it suitable for use on a wide range of substrates. Moreover, the drum format provide more efficient loading for high throughput production. The use of the closed field and unbalanced magnetrons creates a magnetic confinement that extends the electron mean free path leading to high ion current densities. The combination of high current densities with ion energies in the range ~30eV creates optimum thin film growth conditions. As a result the films are dense, spectrally stable, supersmooth and low stress. Films incorporate low hydrogen content resulting in minimal C-H absorption bands within critical infra-red passbands such as 3 to 5um and 8 to 12um. Tuning of germanium carbide (Ge_(1-x)C_x) film refractive index from pure germanium (refractive index 4) to pure germanium carbide (refractive index 1.8) will be demonstrated. Use of film grading to achieve single and dual band anti-reflection performance will be shown. Environmental and durability levels are shown to be suitable for use in harsh external environments.

Multi-dielectric coatings are designed to reach total absorption and maximum field amplification at resonances under total reflection. The design method is analytic and numerical results are given. Comparison with plasmons or thin metallic layers is discussed. Scattering from these coatings is investigated for measurements of amplification.

Thin metal island films exhibit unique optical properties and possess a high potential in design and fabrication of multilayer coatings with sophisticated spectral performances over wide wavelength and angular ranges. Optical properties of these films are dependent on film thickness. In the present study we consider and solve a problem of designing multilayers which reflect different colors from their front and back sides and have specified average transmittance values. Additionally, in many cases the reflected colors are stable to variations of the incidence angle. In the design process we use optical constants of Ag metal island films, that were carefully determined based on recently proposed characterization approach.

During the manufacturing of optical coatings, errors in refractive index values or in thickness values of each layer of the coating can induce dramatic consequences on the desired optical properties. Global numerical sensitivity analyses using space filling designs and metamodels were applied in the case of the influence study of different errors on optical filter characteristics to determine the most critical interactions of layers. We propose to use space filling designs to assess, by computer experiments, the sensitivity of optical filters to the simultaneous errors in the refractive index values and thickness values. In this study, the principal characteristics of space filling designs are presented and are compared to random designs. This comparison allows us to identify the best types of space filling designs to conduct sensitivity analysis with few computer runs. We will present the first results concerning the global sensitivity analysis of different coatings in the case of simultaneous errors in refractive index values and in thickness values. We consider for this study two monitoring techniques: a quartz monitoring and an optical monitoring. By this way, we will highlight the influence of correlated errors on the most critical interactions classification and give a different perspective to these monitoring techniques. In conclusion, this computational study gives clues to the understanding of error propagation in manufacturing processes and points out the most critical interactions in coatings to improve the robustness of optical coatings and to reduce the production costs.

A large number of parameters is often required to describe optical dispersion laws, and it is only through the use of an appropriate global optimization procedure that an accurate thin film index determination can be achieved. In this paper, we propose to investigate the respective performances of three different optimization algorithms, namely Simulated Annealing, Genetic Algorithm and Clustering Global Optimization and compare results with a commercial software dedicated to thin film index determination. This study refers to the single layer and multilayer thin film index determination. It includes the theoretical study of simulated reflection and transmission spectra, and the experimental characterization of Ta₂O₅ single layer and Ta₂O₅/SiO₂ multilayer.

Formulae to estimate the average percent reflectance (Rave) of a broadband antireflection (AR) coating as a function of the bandwidth (B), the overall thickness (C), the index of refraction of the last layer (L), and the difference between the indices of the high- and low-index layers (D) were reported in 1991. Various refinements of these formulae and other insights into the underlying behavior of such coating designs have been reported up until the present time. Dobrowolski, et al.⁶ and Tikhonravov, et al.⁷ have also added independent viewpoints to this subject over this period. In the previous studies, the effects of the index of refraction of the substrate have mostly been ignored and have appeared to be very minor. This study has investigated the influence of the substrate index on the Rave results. It has been found that there seem to be two classes of designs with respect to the effect of substrate index. In the class of "step down" AR designs, there is a significant effect, in the other class, there is no significant effect. Even in the step-down case, there is no effect of substrate index if any and all indices of refraction for the coating materials are available from that of the index of the substrate to the index of the media.

Due to the improvement of deposition technologies and polishing techniques, light scattering has been considerably reduced in optical coatings these last decades, with the result of high quality dense optical filters with minimal losses. However such improvements coupled with modern monitoring techniques have also allowed designing and producing more complex coatings with layer numbers exceeding several hundred in some situations. Within this framework light scattering must again be revisited and analysed in detail, including global loss levels together with angular and spectral analysis. This paper is devoted to the optical balance of sophisticated components for Earth Observation, where the same scene is observed simultaneously in several adjacent wavebands. Self-blocking multilayer stacks are involved to eliminate out-of band harmonics in the instrument but the filter performances are degraded due to an increase of cross talk originating from light scattering. To address this problem we use the theories of light scattering from surface roughness and bulk heterogeneity, which allows to quantity cross-talk levels and choose more adequate filters. A special emphasis is given to the case of hyperspectral filters assemblies located in the focal plane for image filtering.

The robust synthesis based on simultaneous optimization of reflectivity of multiple designs located in a small neighborhood of a pivotal design is presented. Efficiency of this technique is demonstrated by the synthesis and successful experimental realization of two types of high dispersive mirror. The first type of fabricated dispersive mirror covers 690-890 nm wavelength range and provides the dispersion of -300 fs² at 800 nm. We perform 4 independent coating runs to proof reliability of robust design method. The second type of mirror provides -4500 fs² of group delay dispersion in wavelength range 1027-1033 nm.

The environment in space is a particularly harsh one for optical coatings. For porous coatings, space vacuum causes a spectral shift and a resulting change in stress due to water release. Atomic oxygen present in Low Earth Orbits causes erosion of coatings. Space also has a harsh radiation environment which can cause absorptive losses in optics due to colour centre activation. Coatings exposed to solar radiation are subject to UV fixation of outgassing contaminants. Similarly, high power laser irradiation of coatings in the presence of contaminant outgassing sources results in laser-induced contamination, high absorption and potential laser damage. An important effect for high power laser optics is the reduction of the laser-induced damage thresholds of porous coatings in vacuum. An additional factor is the often high thermal excursion coatings can experience in space, typically ranging from -50°C to +80°C, notwithstanding deep space missions which involve cryogenic temperatures where coatings which have to withstand -270°C and coatings to the inner planets which may have to survive temperatures in excess of 300°C. This paper attempts to give a general overview of the effects of the space environment on optical coatings giving some examples from tests carried out by the European Space Agency.

Optical constants for simulations were obtained by R- and T-measurements on TiAlN thin films deposited on Corning 7059 glass. The model parameterized free carrier effects and an inter-band excitation. The calculations demonstrated that the colour effects are due to interference and inter-band absorption around 500 nm in a single layer coating. The peak shifts with the thickness of the thin film which gives a simple way to obtain different colours. Solar absorptance of 86 % can be reached already for a single TiAlN-film on an Al substrate.

We have designed and fabricated the low-polarizing X-plate to increase the luminous throughput for LED projector. We calculate reflectivity characteristic of X-plate as a function of the wavelength at different angles of incidence from air of unpolarized light. A new way to design filter to control the title effect of thin film filters. The wavelength shift of the new design for reflected red filter and reflected blue filter at the angle of 45° ± 8° is 16 nm and 14 nm, respectively.

The operation of thin-disk laser (TDL) systems relies on diode pumping of thin disks of laser active material. The thickness of such laser disks ranges between about 50 and 300 micrometers depending on the absorption coefficient and the number of pump passes. High performance optical coatings deposited on the front and back surface of the disks are essential for efficient TDL operation. Two types of coatings are necessary: On the rear surface, a high finesse HR coating is required to reflect both laser and pumping radiation. On the front surface, a low loss antireflective coating allows to transmit the laser radiation under (near) normal incidence and the pumping radiation under oblique incident angles. Besides the optical properties, the coating system on the TDL substrate has to fulfil specific mechanical and, especially for the HR coating, thermal requirements. At the Laser Zentrum Hannover, a cluster deposition tool has been developed to deposit coatings for TDL systems. This cluster deposition tool consists of a substrate load lock system for inspection and in-situ pre- and post-treatment of the substrates, a second chamber for the deposition of low loss dielectric coatings with Ion Beam Sputtering (IBS) technique, and a third section for the deposition of metal layers, which can be employed as reflective layers or for soldering purposes. The dielectric deposition chamber is equipped with an RF ion source for the deposition of discrete materials or material mixtures. Thus, discrete high low stacks or rugate filter systems can be deposited. The process is controlled via an optical Broad Band Monitor (BBM). Moreover, an in situ stress measurement system based on an online measurement of the bending of the substrate allows for an estimation of the mechanical stress in the material.

Advances in the deposition of metallic thin films are discussed. The ALD growth of ultrathin Ir films is analyzed by transmission electron microscopy, energy dispersive X-ray spectroscopy, atomic force microscopy, and optical and electrical measurements. The morphology of iridium metallic layers is assessed based on Ir/ Al₂O₃ nanolaminate films. High resolution transmission electron microscopy and energy-dispersive X-ray spectroscopy measurements show sharp interfaces and pure Ir layers in the nanolaminates. The iridium films as polycrystalline. Excellent thickness control, high uniformity and low roughness of ALD films are demonstrated. Four point probe measurements of the resistivity of Ir coatings with various thicknesses have been performed and proved conductive layers with an Ir film thickness of ca. 10 nm. The optical properties of the Ir films deposited by ALD are similar to those of the bulk Ir. Thin iridum layers deposited on high aspect ratio linear gratings have been successfully used as electrodes in the electrochemical deposition of gold nanoparticles and gold layers. The gold deposition evolves through the formation of gold islands with ca. 40 nm diameters that coalesce after ca. 60 seconds deposition. The density of the gold islands within the grating pattern is much lower than on the flat region of the substrate. The combination of ALD with electrochemical deposition allows the diversification of conductive layers on complex nanostructured surfaces.

The PluTO project is aimed at combining thin-film and plasma technologies. Accordingly, the consortium comprises experts in optical coating (Laser Zentrum Hannover, Fraunhofer IOF) and such in plasma technology (INP Greifswald, Ruhr University of Bochum RUB). The process plasmas available, especially the sheath layers, will be thoroughly characterized by means of special probes, so that the types, numbers and energies of the particles participating in the coating formation processes can be determined comprehensively in every detail for the first time. The data thus obtained will provide a basis for a numerical modelling of layer growth at atomic scale (Bremen Center for Computational Materials Science BCCMS). The results are expected to deepen the understanding of the physical mechanisms responsible for the influence of plasma action on the layer properties. In parallel, suitable tools for process monitoring will be identified and made available. Some first results have already been achieved which prove the viability of the approach.

Reactive magnetron sputtering was used to deposit optical thin films. In order to obtain high deposition rates, metallic targets were used. For the creation of mixed oxides bipolar pulsed sputtering was applied to two different targets. A new process control setup was developed to monitor the oxidation state of both targets individually. Two different elemental targets are co-sputtered in oxygen-argon atmosphere within the lambda-probe stabilized transition mode. The composition is controlled by optical emission spectroscopy. Thus different mixtures are accessible without changing target material. Varied mixtures in the system hafnia-silica have been prepared. The optical properties (refractive indices, absorption, surface roughness, density) as well as mechanical behavior (film stress, hardness) of the mixtures are compared to pure oxide materials. By mixing the oxides thin film quality can be improved beyond the properties of the single materials.

The deposition of optical precision coatings on glass by magnetron sputtering is still a challenging problem regarding particle density and long term stability of coating plants due to target material erosion. A novel approach to increase process stability and reduce drifts is the usage of cylindrical cathodes. These cathodes allow a particle free deposition process as they have virtually no redeposition zones that can lead to destruction of coatings by arcing caused by surface charges. In the present paper optical single layers as well as multilayer coatings were sputtered by means of reactive magnetron sputtering using a double cylindrical cathode setup. The particle density is determined and compared to particles produced with planar magnetrons. A new sputter coater concept will be presented wherein the magnetrons are attached to a rotating disc coater in a sputter-up configuration. The process was stabilized by means of oxygen partial pressure control. Preliminary optical properties as well as deposition rates of different oxide films will be presented.

In this paper, we present in detail the new deposition magnetron sputtering machine so-called PACA2M, that CILAS has implemented for coating large optics up to 2 meters, within a dedicated consortium, with the financial support of the French Department of Industry and of the local administrations, and with the help and the expertise of the French OPTITEC optical cluster. Our innovative large size deposition machine is equipped with 2.5 meters-long planar magnetrons (seven cathodes), to ensure uniform coating on large optical components, up to 2 meters by 2 meters, 40 centimetres thick and to 1.5 ton weight. Some magnetrons are adapted to a DC, Mid Frequency (MF) or Radio Frequency (RF) operation, which allows the deposition of metals and also dielectric oxides under reactive atmosphere. Moreover, PACA2M is equipped with a powerful broadband optical monitoring system that permits to reach sophisticated spectral specifications and a good agreement with theory, which will be presented in detail in another paper of the conference. As the magnetron sputtering technique leads to very dense layers close to bulk material, it is particularly well suited for applications that require environmental resistance, as for example the LMJ (Laser MegaJoule) French laser fusion program in which CILAS is in charge of the metallic mirrors on large complex-shaped reflectors for laser chains amplifiers. Numerous experimental results are presented here such as protected and enhanced metallic mirrors, metal-dielectric absorbing coatings or multi-dielectric coatings, deposited on different kinds of substrates, for which qualification tests have been done.

A small molecule is a low molecular weight organic compound which is by definition not a polymer. Therefore, physical vapor deposition by evaporation as common for inorganic oxides is often possible. Organic layers can be useful as components of interference stacks for different functions. A number of organic compounds have interesting UV absorption characteristics and can be used to protect UV-sensitive polymers such as polycarbonate. In addition, organic layers can be applied to generate nanostructured thin films with a very low effective refractive index, as shown recently for polymers. A structured organic single layer can be applied as an antireflective (AR) coating for a glass lens. The applicability of several small molecule compounds will be discussed in this paper.

The metal-like electrical conductivity in combination with a high visual transmittance is the characteristic property that opens up a broad spectrum of applications to transparent conductive oxides (TCOs). To fulfill the manifold requirements in each individual case, especially the optical properties of TCOs have to be adapted. The transmittance in the near infrared spectral range can be tailored by a modification of the carrier concentration Ν and mobility μ. The theoretical description for this behavior is based on the well-known Drude theory. Highly conductive indium tin oxide films (ITO) have been prepared by pulsed DC magnetron sputtering. However, due to its excellent electrical properties, the plasma resonance of free carriers occurs near the visual spectral range which results in a very low transmittance in the NIR. In contrast, ITO films with a NIR transmittance of ca. 80% have been prepared by plasma ion assisted evaporation. The combination of high transmittance and low resistivity of ρ=7.4x10^-6Ω was achieved by a decrease of the carrier concentration and a simultaneous enhancement of the electron mobility μ. Secondary, the transmittance of aluminum doped zinc oxide films (AZO) in the UV spectral range could be adapted by changing the doping concentration Ν. This is a direct consequence of the Burstein-Moss shift that leads to a band gap widening dependent on Ν. However, the comparison of the experimental data with theory has shown that the contrary effect of band gap narrowing is not negligible, too.

Thin films consisting of transition metal nanoparticles in an insulating oxide exhibit a high solar absorptance together with a low thermal emittance and are used as coatings on solar collector panels. In order to optimise the nanocomposites for this application a more detailed understanding of their optical properties is needed. Here we use a highly efficient recently developed numerical method to extract the spectral density function of nickel-aluminum oxide (Ni-Al₂O₃) composites from experimental data on the dielectric permittivity in the visible and near-infrared wavelength ranges. Thin layers of Ni-Al₂O₃ were produced by a sol-gel technique. Reflectance and transmittance spectra were measured by spectrophotometry in the wavelength range 300 to 2500 nm for films with thicknesses in the range 50 to 100 nm. Transmission electron microscopy showed crystalline Ni particles with sizes in the 3 to 10 nm range. The spectral density function shows a multi-peak structure with three or four peaks clearly visible. The peak positions are influenced by particle shape, local volume fraction distributions and particle-particle interactions giving rise to structural resonances in the response of the composite to an electromagnetic field.

Ceramic materials such as SiO₂ or Ta₂O₅ are widely used for optical interference coatings. These materials have a high hardness and mostly offer excellent optical properties. However, there is a growing demand not only for good optical properties and a high stability, but also for coatings with a high elasticity. Especially coatings on polymer substrates need layers with improved elasticity since cracks in the layers occur easily when the coated substrates were mechanically deformed. For such applications flexible layer materials using organics or even polymers are very promising. These may be used as pure organic layers of with organic-inorganic composites. Unfortunately the chemical reactions to form polymers layers are more complex than the reactions to form oxides. Thus the deposition techniques for polymer layers are much more varying. Other important issues are the deposition rate stability and the optical properties of the polymer layers like haze, refractive and absorption index. In this paper we compare different ways for the deposition of organic and polymer layers in the gas phase at low pressures. The methods used were: evaporation, sputtering, PECVD and thermal CVD techniques. The optical parameters (refractive index, absorption and haze) and some mechanical parameters (adhesion, crack onset strain) of the different polymer layers were characterized. It will be shown that excellent organic film properties can be obtained by the use of a suitable organic material and deposition process. Also shown will be results on composite materials to modify the optical properties.

IRDIS (Infra Red Dual Imager and Spectrograph) is one of the scientific sub-systems for the SPHERE (Spectro-Polarimetric High-contrast Exoplanet REsearch) instrument, to be mounted on one of the four VLT 8-m telescopes in Paranal (Chile) in 2012. IRDIS and two other scientific sub systems will analyze the resulting high-contrast image with the aim of direct detection of extrasolar planets. IRDIS covers the near infrared bands Y, J, H and Ks (950-2300nm) and works at cryogenic temperature. The main observational mode of IRDIS is Dual Band Imaging, where the same object is observed simultaneously in two adjacent wavebands. For this mode, differential aberrations between the two channels are critical and filter optical quality is crucial. In this paper, we focus on the design, production and tests of the IRDIS filters. The deposition technique involves DIBS (Dual Ion Beam Sputtering) and leads to very compact coatings, with material properties close to those of bulk material, making these filters well suited for cryogenic applications. The use of an in-situ optical monitoring system in visible and near infrared range (up to 2500nm) permits to reach the demanding spectral filter specifications (bandwidth, rise and fall widths, peak transmission, wide band blocking) and to have a good agreement with the theoretical design. Spectral measurements at ambient and cryogenic temperatures are then presented.

For more than four decades band-pass filters are important components of microscopes used for the fluorescence spectroscopy. During all the time this special field of application has been one of the main drivers for research and development in thin-film optics, particularly for the thin-film design software and the coating technology. With a shortwave pass filter, a multi-notch filter, and a classical band-pass filter as examples of such filters provided for the latest generation of fluorescence microscopes we present the state-of-the-art in coating design and technology. Manufacturing these filters is a great challenge because the required spectral characteristics need necessarily multilayers with up to 300 layers and overall thicknesses up to 30 μm. In addition, the designs require also 3 to 5 nm as thinnest layers and all the layers are completely of non-quarterwave type. The filters were manufactured in a rapid-prototyping regime by a Leybold Helios plant using plasma-assisted reactive magnetron sputtering of thin films of different metal oxides. Designed and real spectra are compared and differences are discussed. Measurement results of other optical and non-optical characteristics as film stress, total integrated scattering, and micro roughness are presented.

Besides the typical channels in the visible and near infrared spectrum, optical remote sensing of the earth from air and space utilizes also several channels in the short-wave infrared spectrum from 1000 nm to 3000 nm. Thin-film optical filters are applied to select these channels, but the application of classical multiple-cavity band-pass filters is impossible. Because of their additional blocking elements they are disallowed due to geometrical or other non-optical reasons. Within the sensitivity region of an MCT detector as typical detector device, the selection and blocking of radiation by the filter has to be provided by a single multilayer system. The spectral region of the SWIR as well as blocking width and depth require necessarily designs with overall thicknesses of more than 20 μm, with layer numbers up to 100. SiO₂ and TiO₂ were used as thin-film materials deposited with reactive e-beam evaporation under ion assistance in a Leybold SyrusPro box coater. A special challenge was the thickness measurement of the thin films by an optical broadband monitoring device in the visible range. The results of manufacturing and characterizing of such filters are presented by three examples for the center wavelengths of 1375 nm, 1610 nm, and 2190 nm.

High performance infrared polarizing beam-splitters (PBS) with broad bands and wide angular fields are required for IR applications that use both transmitted and reflected polarizing beams equally from 3 to 14 μm. Existing infrared wire grid polarizers do not meet the requirements because they have good performance only in transmission, not in reflection. No practical IR PBS devices are yet available for this spectral region. In this paper, we propose to fabricate an infrared thin film polarizing beam-splitters based on previously described light interference and frustrated total internal reflection. The PBS coatings consist of Ge and fluorite layers on ZnSe prism substrates. Similar high performance PBS designs have been successfully made in the visible. However, it is more challenging to make such PBSs in the infrared region, mostly due to the use of soft IR coating materials, the low energy evaporation process and the optical contacting bonding technique. In the paper, we will report for the first time the measured performance of a prototype IR PBS for the 7-13 μm spectral region with an angular field ±7.82° in air. We will also discuss the challenges in fabricating the prototype PBS, including optical constant characterization and device measurements.

The behaviour of interference optical filters for space applications has been investigated under low- and high-energy proton irradiation. Low-energy protons are expected to be necessary to prove the effects on the coating, whereas the high-energy proton tests shall verify mainly the substrate susceptibility to induced damage. The expected interaction of protons with coating and substrate was simulated by software, to identify the most appropriate conditions for the irradiation experiments. Two different accelerator facilities were used for low- and high- energy protons: 60 keV protons with an integrated fluence of 10¹² p⁺/cm² and 30 MeV protons with an integrated fluence of 10⁸ p⁺/cm². The spectral transmittance of the filters was measured before and after irradiation and, according to simulations, no significant effects were detected in the visible-near infrared spectrum, while some variations appeared at short wavelengths with low-energy irradiation.

We report an experimental investigation in the laser-induced damage threshold (LIDT) of optical coatings materials. The samples are single layers of Al₂O₃, Nb₂O₅, HfO₂, SiO₂, Ta₂O₅, ZrO₂ deposited through different deposition techniques (evaporation or sputtering with/without ion assistance) and mixtures of Al₂O₃/SiO₂, Nb₂O₅/SiO₂, HfO₂/SiO₂, Ta₂O₅/SiO₂ and ZrO₂/SiO₂ on silica substrates. The LIDT is measured at 1030nm, 500fs in single shot mode. The results are expressed and compared in term of LIDT as a function of bandgap and LIDT as a function of refractive index.

Nodules have been proved to play an important role in the activation of laser damage in 1.053 μm HfO₂/SiO₂ high reflectors. However, some damage test results revealed that the ejection fluences of some big nodules with height around 1 μm were abnormally high. To find the correlation between the surface dimensions of nodules and their susceptibility to nano-second pulsed laser radiation, monodisperse SiO₂ microspheres with five different sizes were used to create engineered nodules in 1.053 μm HfO₂/SiO₂ high reflectors. The defect density of nodules that were created from SiO₂ microspheres was purposely controlled to be around 20-40 mm² and special care was taken to minimize clusters of SiO₂ microspheres as less as possible. This enabled us to take a raster scan test and to get the statistical value of ejection fluences of these engineered nodules. The height and width dimensions of the engineered nodules, especially the discontinuity of nodular boundary, were measured by cross-sectioning of nodular defects using a focused ion-beam milling instrument. Based on the above information, the damage test results were interpreted from the aspects of electric field enhancement model and mechanical stability of nodular structures.

We present the design, the optimization and the realization of multilayer mirrors for the transport and the compression of attosecond pulses generated by high harmonics emission from 35 eV to 55 eV. At wavelength characterizations have been performed on an attosecond source. We explore also the phase determination of the complex reflectivity from photon-electron emission measurement on synchrotron beamline.

We have developed and elaborated a series of Mg/Co-based periodic multilayers to build efficient mirrors for the extreme ultraviolet (EUV) range. For s-polarized light and at 45° of grazing incidence, the reflectivity of as-deposited Mg/Co is 42.6% at 25.1 nm. X-ray emission spectroscopy and nuclear magnetic resonance measurements do not indicate any noticeable interdiffusion at the interfaces between layers. Scanning transmission electronic microscopy images attest the high structural quality of the stack. X-ray reflectivity (XRR) curves in the hard x-ray and EUV domains confirm this description and estimate a weak interfacial roughness (~ 0.5 nm). Taking advantage of the magnetic character of Co, we have performed resonant magnetic reflectivity measurements by scanning the photon energy around the Co L absorption edge for opposite circular polarizations. The magnetization profile of the Co layers within Co/Mg determined with an expected depth resolution of one monolayer confirms the interface abruptness. Scanning electron microscopy images and XRR curves give evidence of the thermal stability of Mg/Co up to 300 °C. From that value, a strong change in the sample morphology due to the delamination of the multilayer from the substrate occurs. This should account for the drastic reflectivity drop observed above this temperature. Starting from Mg/Co, we have inserted a Zr layer at one or at the other interface or at both interfaces to estimate the effect of the introduction of a third material within the period. We have found that Mg/Co/Zr is more efficient (50% of reflectivity) than Mg/Zr/Co and Mg/Zr/Co/Zr (~ 40%). Through time-of-flight secondary ion mass spectrometry depth profiling and NMR measurements, we have assigned this difference to an intermixing process when Co layers are deposited onto Zr layers.

We report on further development of three-material multilayer coatings made with a use of aluminum for the extreme ultra-violet (EUV) applications such as solar physics, high-order harmonic generation or synchrotron radiation. It was found that an introduction of refractory metal in Al-based periodic stack helps to reduce significantly an interfacial roughness and provides for a higher theoretical reflectance in the spectral range from 17 to 40 nm. The normal incidence reflectivity as high as 55 % at 17 nm, 50 % at 21 nm and 42 % at 30 nm was achieved with the new Al/Mo/SiC and Al/Mo/B₄C multilayer mirrors, which have been optimized, fabricated and characterized with x-rays and synchrotron radiation. A good temporal and thermal stability of the tri-component Al-based multilayers has been observed over 3 years.

Little development on coatings has been available in the 50-120-nm spectral range until recently. One main reason for this is the large absorption of most materials in nature in this range. Our group has followed a research towards the development of novel coatings for this spectral range. This research has been based on the search and characterization of new materials mainly with low absorption. For many materials we have performed their optical characterizations in a large spectral range to reduce common inconsistencies that arise when combinations of data from different sources are used. We summarize our research on the characterization of many lanthanides, among other materials. Lanthanides are particularly interesting because they have a relatively low absorption in the spectral range of interest. Self-consistent characterization of other materials, such as SiC and B₄C, has been performed for their interest as candidate materials for coatings involving the EUV to the visible. The discovery in lanthanides of a wealth of materials with relatively low absorption has enabled the development of multilayers based on the low absorption of Yb and Eu lanthanides. This resulted in the first narrowband multilayers with a peak wavelength in the 70 to 100 nm. We also report recent research on the development of multilayers with a peak reflectance above 100 nm; these multilayers address two targets: a) narrowband performance; b) zero reflectance at a wavelength slightly longer (such as 121.6 nm) than the peak wavelength. As for a), a promising preliminary result is obtained with a narrowband multilayer peaked at 101 nm. Regarding b), multilayers with a high reflectance at 102.6 nm and a low reflectance at 121.6 nm were prepared and they displayed a successful performance when measured in situ (not exposed to the atmosphere); however, the minimum at 121.6 nm was lost after a short exposure to air. The latter research is still underway and we plan to experiment with new designs. Our group has also prepared efficient narrowband transmittance coatings peaked at wavelengths longer than 120 nm. They are based on the classical combination of Al and MgF₂.

We have investigated the optical properties and thermal stabilities of a serial of Mg-based multilayers including Mg/SiC, Mg/Co and Mg/Zr in extreme ultraviolet (EUV) range. Mg/X multilayer mirrors were deposited by magnetron sputtering technique onto polished silicon wafers. In order to study their stabilities under heat resistance, annealing experiments were carried out in vacuum environment keeping 1hour at different temperatures from 200°C to 550°C. Their EUV reflectivities were measured by using synchrotron radiation. Grazing incident X-ray and EUV reflection measurements were used to estimate the thermal stability of these multilayer systems. Mg/SiC and Mg/Co are stable up to 200°C and the reflectivity decreases drastically with the increase of temperature, while the reflectivity of Mg/Zr keeps constant during annealing at 300°C and falls slowly as the temperature increases. Up to 550°C, Bragg peaks of Mg/Zr multilayer are still sharp in X-ray reflectivity curve, and EUV reflectivity is 25% at 26.2nm at 30 degree incidence. These measurement results indicate that Mg/Co and Mg/SiC should be used in application requiring no heating above 200°C, while the new material combination Mg/Zr is a promising multilayer for practical application requiring stronger heat resistance in EUV range.

Modern efficient optimization techniques, namely needle optimization and gradual evolution, enable one to design optical coatings of any type. Even more, these techniques allow obtaining multiple solutions with close spectral characteristics. It is important, therefore, to develop software tools that can allow one to choose a practically optimal solution from a wide variety of possible theoretical designs. A practically optimal solution provides the highest production yield when optical coating is manufactured. Computational manufacturing is a low-cost tool for choosing a practically optimal solution. The theory of probability predicts that reliable production yield estimations require many hundreds or even thousands of computational manufacturing experiments. As a result reliable estimation of the production yield may require too much computational time. The most time-consuming operation is calculation of the discrepancy function used by a broadband monitoring algorithm. This function is formed by a sum of terms over wavelength grid. These terms can be computed simultaneously in different threads of computations which opens great opportunities for parallelization of computations. Multi-core and multi-processor systems can provide accelerations up to several times. Additional potential for further acceleration of computations is connected with using Graphics Processing Units (GPU). A modern GPU consists of hundreds of massively parallel processors and is capable to perform floating-point operations efficiently.

Enhanced strategies in optical broadband monitoring allow for thin film deposition under rapid production conditions with very high process stability. Recent developments in the field include simulation techniques with virtual deposition systems, to enable a pre-selection of different multilayer designs, and hybrid process control strategies which combine optical monitoring with quartz crystal monitoring. In particular, automated online error re-calculation and design re-optimization are presently in the focus of research to improve the efficiency of deposition plants. In this contribution a developed re-optimization module is presented, and the resulting increase in production yield of complicated multilayer designs is demonstrated by deposition examples. Besides automated design changes directly initiated by the re-calculation software, the presented approach also considers supervising functions that stop the deposition run when critical errors are detected.

Ever increasing demands in the field of optical coating systems with highest complexity impose new challenges on the development of advanced deposition techniques with increased stability, and especially on the corresponding precise thickness monitoring strategies. Most of the classical thickness monitoring concepts employed in industrial production, which are based on quartz crystal or optical monitoring, are presently operated near to their precision limits. However, resulting from extensive research activities, monitoring concepts could be significantly extended during the last years. On the one hand, newly developed hybrid process control algorithms combine the information of the optical and non-optical sensors to achieve a higher precision and fault-tolerance. On the other hand, independent thickness monitors are integrated in flexible manufacturing concepts which include adapted computational manufacturing tools as well as specific re-calculation and design re-optimization modules. Computational manufacturing allows for a design pre-selection prior to deposition with essentially improved certainty which could not be achieved with classical error analysis until now. In contrast, the re-calculation and re-optimization modules are on-line tools that monitor the running deposition process. In case of critical deviations, a fully automated modification of the residual design assures a successful achievement of specifications under the chosen monitoring technique.

In the field of optical coatings production, in situ determination of thin films properties during deposition process is a key point for the achievement of high performance filters. Using a spectral measurement over a wide range is a way to improve the robustness of the reverse engineering methods implemented for the monitoring of thin film thickness and the in-situ determination of material refractive index. In the framework of the development of a magnetron sputtering deposition machine for 2-meter optics driven by CILAS, the Optical Thin-Film Research group of Institut Fresnel has designed and qualified a dedicated Broadband Optical Monitoring covering the visible and near infrared spectral range from 280 nm to 2 200 nm. An all-fibered system, well adapted to the extremely large size of the machine, is used to select the location of the measurement point inside the vacuum chamber (among 9 possible). Moreover, this system allows to achieve uniformity studies at the surface of large size substrates along a straight line perpendicular to the cathode main axis with the help of the motorized displacement system of the substrate in front of the magnetron cathodes. A real-time monitoring of the physical thickness is thus done offering possibilities for automatic deposition process and in-line design re-optimization.

In this work we want to demonstrate how the methodology of Design of Experiment (DOE) can be used for the development of ion-assisted ITO films deposited at low temperatures. The optimization method allows us to identify the process parameters, which yield films with high transmittance and low resistivity. The article will show the results obtained for transmittance and resistivity. Furthermore, the dispersion of the refractive index and the extinction coefficient will be determined as well as the surface roughness. In ITO there is a trade-off between transmittance / absorbance and sheet resistance. Virtually absorption free films could be obtained with a resistivity of 3.2 μΩm, whereas the lowest resistivity (2.7 μΩm) yielded a transmittance, which was reduced by a few percent.

This paper describes a method for modelling film thickness variation across the deposition area within plasma enhanced chemical vapour deposition (PECVD) processes. The model enables identification and optimization of film thickness uniformity sensitivities to electrode configuration, temperature, deposition system design and gas flow distribution. PECVD deposition utilizes a co-planar 300mm diameter electrodes with separate RF power matching to each electrode. The system has capability to adjust electrode separation and electrode temperature as parameters to optimize uniformity. Vacuum is achieved using dry pumping with real time control of butterfly valve position for active pressure control. Comparison between theory and experiment is provided for PECVD of diamond-like-carbon (DLC) deposition onto flat and curved substrate geometries. The process utilizes butane reactive feedstock with an argon carrier gas. Radiofrequency plasma is used. Deposited film thickness sensitivities to electrode geometry, plasma power density, pressure and gas flow distribution are demonstrated. Use of modelling to optimise film thickness uniformity is demonstrated. Results show DLC uniformity of 0.30% over a 200 mm flat zone diameter within overall electrode diameter of 300mm. Thickness uniformity of 0.75% is demonstrated over a 200mm diameter for a non-conformal substrate geometry. Use of the modelling method for PECVD using metal-organic chemical vapour deposition (MOCVD) feedstock is demonstrated, specifically for deposition of silica films using metal-organic tetraethoxy-silane. Excellent agreement between experimental and theory is demonstrated for conformal and non-conformal geometries. The model is used to explore scalability of PECVD processes and trade-off against film thickness uniformity. Application to MEMS, optical coatings and thin film photovoltaics is discussed.

For the production of high performance multilayer systems with tight specifications and large numbers of layers optical monitoring is essential. Substantial progress was achieved by the introduction of direct monitoring on the rotating substrate holder. Pre production analysis by computer simulation of coating processes helps to optimise monitoring strategies and reduces the effort for expensive and time consuming test runs significantly. However not in any case we can find error compensating monitoring strategies. Also we have to deal with error accumulation effects especially with multi layer systems with large number of layers. Changing the monitor glass after the layer stack is deposited partly is a useful method to discontinue accumulation or to simplify the monitoring strategy. A testglass changer which helps to suppress error accumulation was developed and automized. The testglasses are located on the rotating substrate holder which may be a calotte or a plane substrate holder. It combines the advantages of direct monitoring with the flexibility to change testglasses in a fully automatic process. The basic principle will be described. Results of multilayer systems demonstrate the benefits of the newly developed testglass changer.

Our recent theoretical and experimental investigation of the photothermal effect in a planar metamaterial absorber is reviewed in the present paper. The observed ultrasensitive photothermal heating in such an absorber nanostructure irradiated by a pulsed white-light source is elaborated with a simple yet compelling heat transfer model, which is subsequently solved with a finite-element method. The simulation results not only agree with the experimental finding, but also provide more detailed understanding of the temperature transition in the complex system.

A critical feature of one-dimensional photonic crystals (omnidirectional reflectors) is an existence of bandgaps where both transverse electric (electric field perpendicular to the plane of incidence) and transverse magnetic (magnetic field perpendicular to the plane of incidence) polarizations of impinging light are totally reflected for any incident angle. In this paper it is shown that omnidirectional bandgaps of binary (two layers in the unit cell) crystals might be increased when each cell is modified by a third layer with the refractive index value in between of the refractive indices of two layers constituting the original cell.

In this article, we predicted the optical properties of the thin film including quantum dots according to the mathematic mode which is based on the quantum theory. The method consists of two parts. The first one is the classical explanation for the interaction between light and matters. It takes care of the interaction as dipoles and electromagnetic wave and describes clearly the profile of spectrum. Another part is the transition of quantized energy, absorption and spontaneous emission which exhibits singular valleys or peaks in spectrum. For the reason of quantum theory, we have to verify Bohr radius of each crystallized material to make sure that the particle size is small enough to present quantum effect. After constructing the spectrum, the data significantly presents optical properties of matters, we try to re-define the effective refractive index of the thin film including quantum dots by the spectrum which is the result of light affected by matters.

It is shown how the discussion about antireflection coatings for the visible and near infrared region has been changed dramatically with recent experimental applications of nanostructures that realize media with effective refractive indices less than the 'magic border' of 1.34. Using the so-called binary optics as an example, a glass-like nanostructure similar to the moth-eye structure is theoretically designed as antireflection coating for the visible and near infrared region. With the aim of this example and considering only known design principles of thin-film optics, a connection between nanostructures and thin films regarding their alternative or combined application as antireflection coatings is presented. As summary regarding the nanostructures vs. thin film discussion, a reference list is presented that cited different types of antireflection coatings presented in the past 70 years with respect to their applications, designs, and deposition technologies.

Self-focusing of optical Gaussian pulse with the axial-symmetric profile of the beam due to cascading SHG at the big phase mismatch in the layered photonic crystal is considered. We show the possibility of strong self-focusing of the optical radiation in such conditions: a maximum intensity increases 70 (and more) times in comparison with the intensity of incident optical beam. Gaussian profiles of beam and Gaussian shape of pulse are preserved with sufficient good accuracy in the section of first or second nonlinear focus realization. These characteristics of optical radiation remain the same after leaving the pulse of the photonic crystal. For corresponding choice of interaction parameters the losses of energy at fundamental wave because of its conversion to the wave with double frequency is less than 5%. An influence of the incident intensity of laser pulse and the crystal length on the process of self-focusing is investigated also.

Gravitational wave detectors such as Virgo and LIGO use long-baseline Michelson interferometers with high finesse Fabry-Perrot cavity in the arms. The symmetry of these cavities is essential to prevent the interferometer from sensitivity to laser fluctuations. For this purpose the difference between the transmissions of the two input mirrors has to be minimized. Advanced LIGO, the upgrade of LIGO, plans a transmission matching between the two input mirrors as high as 99%. A small deviation in the process fabrication from run to run might induce transmission mismatch larger than 1%. Consequently, the two input mirrors have to be coated during the same coating run. That requires ability to deposit the reflective coating, based on a stack of titanium doped tantala (Ti:Ta₂O₅) layers and silica layers, uniformly over a 800 mm diameter aperture. This paper presents the study to improve the thickness uniformity of a reflective coating and the preliminary results achieved on two Ø350mm substrates coated in the run.

In this paper, we present the development of Al-based multilayer mirrors for the spectral range [17 nm - 34 nm]. The purpose of presented study is to optimize the deposition of Al-based multilayers by the ion beam sputtering (IBS) technique according to several parameters such as the ion beam current and the angle of inclination of targets, which allowed us to vary the energy of ad-atoms deposited onto a substrate. We expected to achieve good reflectivity values for both two- and three-material stacks: aluminum/molybdenum Al/Mo, aluminum/molybdenum/boron carbide Al/Mo/B4C and aluminum/molybdenum/silicon carbide Al/Mo/SiC. We have undertaken a series of structural and chemical analyses of these systems. We present their optical characteristics in the EUV range.

The ideology of a photonic crystal resonator covered with optically nonlinear layers is proposed for binary adder and logic gates of various kinds. The all-optical way to transform a physically added sequence of signals into the logical sequence with corresponding shift of digital units is based on the nonlinear band shift effect. In this work, the electromagnetic field structure for optically linear 1D porous silicon photonic crystal is investigated. The optical parameters of a 1D photonic crystal resonator built on layered porous silicon covered with a nonlinear layer are calculated for various nonlinear materials. An approximate design of an all-optical adder based on 1D porous silicon resonator is considered. The adder heating by powered optical pulses and energy distribution inside the device are analyzed and the problem solution with the use of special semitransparent redirecting mirrors is proposed. It was found that from the point of view of heating the R-scheme of signal processing is more optimal.

Many fields of high technology take advantage of conductor-dielectric interface properties. Deeper knowledge of physical processes that determine the optical response of the structures containing metal-dielectric interfaces is important for improving the performance of thin film devices containing such materials. Here we present a study on optical properties of several ultrathin metal oxides deposited over thin silver layers. Some widely used materials (Al₂O₃, SiO₂, Y₂O₃, HfO₂) were selected for deposition by r.f. sputtering, and the created metal-dielectric structures with two of them, alumina and silica, were investigated in this work using attenuated total reflectance (ATR) technique and by variable-angle spectroscopic ellipsometry (VASE). VASE was performed with a help of a commercial ellipsometer at various incident angles and in a wide spectral range. A home-made sample holder manufactured for WVASE ellipsometer and operational in Otto configuration has been implemented for angle-resolved and spectral ATR measurements. Simultaneous analysis of data obtained by these two independent techniques allows elaboration of a representative model for plasmonic-related phenomena at metal-dielectric interface. The optical constants of the interface layers formed between metal and ultrathin oxide layers are investigated. A series of oxides chosen for this study allows a comparative analysis aimed for selection of the most appropriate materials for different applications.

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.

Optical filters are used for a variety of purposes at astronomical telescopes. In the near infrared region, from 0.8 to 2.5 μm, bandpass and edge filters are used to separate the different astronomical channels, such as the J, H, and K bands. However, in the same wavelength range light emission generated in the earth's atmosphere is superimposed on the stellar radiation. Therefore, ground based astronomical instruments measure, in addition to the stellar light, also unwanted contributions from the earth's atmosphere. The characteristic lines of this OH emission are extremely narrow and distributed over the complete NIR spectral range. The sensitivity of future telescopes, like the European Extreme Large Telescope (E-ELT) which is currently being designed by ESO, can be dramatically improved if the atmospheric emission lines are effectively suppressed while the stellar radiation is efficiently transferred to the detector systems. For this task, new types of optical filters have to be developed. In this framework new design concepts and algorithms must be used, combining the measurement needs with practical restrictions. Certainly, the selected deposition process plays the key role in the manufacturing process. Precise and highly stable deposition systems are necessary to realise such filter systems with an appropriate homogeneity. Moreover, the production control techniques must be adapted to match the high level of precision required in the NIR range. Finally, the characterisation set-ups for such filters systems have to be provided. The manufacturing of such a filter system for a feasibility study of an E-ELT instrument is presented. The design development, the deposition with adapted Ion Beam Sputtering deposition plants, and the characterisation of such filters in the J-Band is described.

The purpose of this research was to compare the optical properties and structure of tungsten oxide (WO₃) thin films that was deposited by different sputtering depositions. WO₃ thin films deposited by two different depositions of direct current (DC) magnetron sputtering and pulsed DC sputtering. A 99.95% WO₃ target was used as the starting material for these depositions. These WO₃ thin films were deposited on the ITO glass, PET and silicon substrate by different ratios of oxygen and argon. A shadow moiré interferometer would be introduced to measure the residual stress for PET substrate. RF magnetron sputtering had the large residual stress than the other's depositions. A Raman spectrum could exhibit the phase of oxidation of WO₃ thin film by different depositions. At the ratio of oxygen and argon was about 1:1, and the WO₃ thin films had the best oxidation. However, it was important at the change of the transmittance (ΔT = T_bleached - T_colored) between the coloring and bleaching for the smart window. Therefore, we also found the WO₃ thin films had the large variation of transmittance between the coloring and bleaching at the gas ratios of oxygen and argon of 1:1.

Residual or internal stresses directly affect a variety of phenomena including adhesion, generation of crystalline defects, perfection of epitaxial layers and formation of film surface growths such as hillocks and whiskers. Sputtering oxide films with high density promote high compressive stress, and it offers researchers a reference if the value of residual stress could be analyzed directly. Since, the study of residual stress of SiO₂ and Nb₂O₅ thin film deposited by DC magnetron sputtered on hard substrate (BK7) and flexible substrate (PET and PC). A finite element method (FEM) with an equivalent-reference-temperature (ERT) technique had been proposed and used to model and evaluate the intrinsic strains of layered structures. The research has improved the equivalent reference temperature (ERT) technique of the simulation of intrinsic strain for oxygen film. The results have also generalized two models connecting to the lattice volume to predict the residual stress of hard substrate and flexible substrate with error of 3% and 6%, respectively.

High reflecting multilayer coatings play a key role for many applications of pulsed Nd:YAG high power lasers in industry and science. In the present contribution, improvements in the optical properties and the radiation resistance of high reflectors for 355nm and 1064nm wavelength on the basis of mixture materials are discussed. Within a co-operation between the LASEROPTIK GmbH and the Laser Zentrum Hannover e.V., several deposition processes including Ion Beam Sputtering, Magnetron Sputtering, and Electron Beam Evaporation could be addressed for this study. The selected material combinations HfO₂+ZrO₂/SiO₂, HfO₂+Al₂O₃/SiO₂, HfO₂+SiO₂/SiO₂ and HfO₂/SiO₂ were deposited using a zone target assembly for the IBS technique or defined material mixtures for the evaporation process. Single layers of the applied mixtures were analyzed by UV/Vis/NIR spectroscopy to correlate the optical constants with the atomic compositions quantified by Energy Dispersive X-ray Spectroscopy (EDX) and X-ray Photoelectron Spectroscopy (XPS). In addition to pure material reference mirrors and reflecting multilayer coatings with high index material mixtures, also interference coatings consisting of nanolaminates as well as multilayer systems with refractive index profiles were produced. The laser induced damage thresholds at 1064nm wavelength for nanosecond pulse durations were measured in a 1000on1 experiment complying with the standard ISO11254. For the 355nm high reflectors, the radiation resistance was determined in a 10000on1 procedure, furthermore, the radiation-induced absorption was measured by laser calorimetry according to ISO11551. Finally, the layer interfaces and the amorphous microstructure of selected multilayers were analyzed by Transmission Electron Microscopy (TEM) to obtain detailed information about possible partial crystallinity. The results are interpreted in the context of former investigations on the power handling capability of coating systems involving material mixtures.

Our approach consists in finding the eigenmodes and the complex eigenfrequencies of structures using a finite element method (FEM), that allows us to study mono- or bi-periodic gratings with a maximum versatility : complex shaped patterns, with anisotropic and graded index material, under oblique incidence and arbitrary polarization. In order to validate our method, we illustrate an example of a four layer dielectric slab, and compare the results with a specific method that we have called tetrachotomy, which gives us numerically the poles of the reflection coefficient (which corresponds to the eigenfrequencies of the structure). To illustrate our method, we show the eigenvalues of one- and two-dimensional gratings.

Ion beam sputtering (IBS) is a well-established process to manufacture lowest loss coatings of highest complexity of spectral behavior. Nevertheless, the losses due to absorption in the bulk materials are still orders of magnitude lower than in the corresponding coatings, indicating that a further optimization of the process is possible. Such an improvement in quality requires a more detailed knowledge of the correlation between the process parameters and the coating quality. The present paper reports on a preliminary study based on a parameterization strategy for IBS processes. The propagation properties of the ion beam were investigated in detail, where both, the total dissipation of energy and the argon ion velocity distribution of the beam were measured and analyzed. Furthermore, research was concentrated on the sputtered material considering the dependence of the optical losses of the deposited dielectric layers on the physical properties of the adatoms. The energy distribution and the charge state of the material particles were investigated with respect to the implementation of a phase separating IBS process.