This PDF file contains the front matter associated with SPIE Proceedings Volume 7101, including the Title Page, Copyright information, Table of Contents, and the Conference Committee listing.

The field of Optical Coatings is sometimes described as a mature technology, the sense being that not much new is actually happening. Nothing could be further from the truth. It is true that optical coatings have been with us for a long time, but the rate of innovation continues to show constant acceleration. The nature of optical coatings implies that they largely respond to needs from the entire field of optics where they enable advances rather than spearhead them. A modern camera lens would be a poor performer without the optical coatings that reduce glare and improve transmittance. Each DVD reader contains a number of optical coatings without which it could not function. These are just two examples of advances in applications of optics driving coating developments. The talk will trace some aspects of progress in coatings from the early days of the 16th Century, when Venice was the center for mirror production, to the worldwide production of the present day. It will survey some current demanding applications and discuss some of the latest innovations. Each advance requires the solution of new problems that are almost invariably a complex mixture of optics, materials science, chemical, mechanical and electrical engineering and often much more. The future of optical coatings is the future of optics itself.

It is shown that most of the known AR coatings that start with the famous quarter-half-quarter coating including the multi-cycle designs display simply alternative solutions to replace unavailable refractive indices of a standard solution. On the basis of this viewpoint some design principles are presented that help to derive an approach to solve a given AR problem. Principal objective of the presented approach is the application of previously defined terms 'equivalent substrate index' and 'equivalent stack index' that characterise a quarter-wave optical thickness multilayer system. It is shown that the presented design principles are also suitable if, instead of a thin-film system, a modification of the interface is used to reduce the surface reflection.

A semi-empirical formula for estimating numbers of layers of broadband antireflection (AR) coatings is presented. Numbers of layers providing by this formula are in the excellent agreement with results of multiple computational experiments on designing of AR coatings for various combinations of refractive indices and boundary wavelength ratios of AR spectral regions.

Optical coatings are subject to random and systematic errors. Assuming unvarying dispersion, least-squares fitting of measured spectra provides means to solve for non-gross thickness errors. Unlike coating design, in which many acceptable and nearly equivalent solutions are possible, inverse-synthesis requires the unique and correct solution. We introduce a 'Gedankenspektrum' (thought spectrum) method for determining the range and types of spectra required for a correct solution. Starting with an ideal design, we simulate production errors and then calculate the spectrum. Returning to the original design, we solve for the layers corresponding to the modified spectrum. Finally, if each layer is close to its known value, inverse-synthesis is successful; otherwise it fails. The process is repeated until the statistics become clear. Reliability depends on the type of design, number of layers, and measurement specifics. Most importantly, reliability increases markedly when measurements at non-normal incidence are included. This indicates the insufficiency in the (usual?) practice of measuring optical coatings solely according to pass/fail criteria. A second 'Gedankenspektrum' method helps decide which spectral measurements and film thicknesses are required for determining n&k in single films, particularly metals. Starting with given dispersion values, random noise is added to calculated spectra, thereby simulating measurement conditions. We then solve for n&k and compare to given values.

A Fourier frequency filtering approach is applied to thin film design in situations well exceeding the theoretical limits of the conventional Fourier transform method. Previous work is generalized to oblique incidence. Examples of a high-reflectance filter and a broadband, wide-angle antireflection coating are given.

A new technology based on plasma etching has been developed to produce antireflective surface structures. By choosing thin initial layers and variable plasma conditions, a broad range of nanostructures can be obtained on various polymers. A broadband antireflective effect can be achieved that is less sensitive to the incident angle of light compared to multilayer interference coatings. Thin layers of silica help in mechanical protection, especially if the structured surface is nearly enclosed by the protection layer. In addition, surfaces that show both antireflective properties and an antifogging effect have been prepared. Combinations of SiO₂ and fluorine-containing layers were found to be useful in obtaining super-hydrophobic behavior. This advanced plasma etching is not limited to a special plasma source and the suitability of different plasma sources is discussed.

"Closed field" magnetron (CFM) sputtering offers a flexible and high throughput deposition process for optical coatings and thin films. CFM sputtering uses two or more different metal targets to deposit multilayers comprising a wide range of dielectrics, metals and conductive oxides. Moreover, CFM provides a room temperature deposition process with high ion current density, low bias voltage and reactive oxidation in the entire volume around the rotating substrate drum carrier, thereby producing films over a large surface area at high deposition rate with excellent and reproducible optical properties. Machines based on the Closed Field are scaleable to meet a range of batch and in-line size requirements. Typically, thin film thickness control to <±1% is accomplished simply using time, although optical monitoring can be used for more demanding applications. Fine layer thickness control and deposition of graded index layers is also assisted with a specially designed rotating shutter mechanism. This paper presents data on optical properties for CFM deposited optical coatings, including anti-reflection, thermal control filters, graded coatings, narrowband filters as well as conductive transparent oxides such as indium tin oxide and carbide films. Benefits of the CFM sputter process are described.

The deposition of oxide coatings with excellent optical and mechanical properties requires powerful plasma or ion sources. We investigated the layer performance of oxide coatings using a large aperture radio frequency powered plasma source for plasma ion assisted application and related the achieved coating performance to beam parameter of the source. The coatings exhibit low compressive stress values, high refractive indices and low absorption values. Using the new type of source in combination with direct optical monitoring on the dome for the production of challenging interference filters shows a huge potential in terms of stability, running costs and easy maintenance. Examples of application in the visible spectral region will be given.

Reactive magnetron sputtering processes have gained considerable interest for the production of precision optical coatings. Pulsed sputtering techniques allow the deposition of high quality optical materials at high deposition rates. However, under high throughput conditions and with tight spectral tolerances, process stabilization has to be included in the fabrication process. Normally, pulsed magnetron sputter techniques are typically characterized by a low ionization. Very recently, ionized magnetron sputtering techniques are under investigation, where either the reactive gas or the metallic sputtered particles are highly ionized. Plasma assisted reactive magnetron sputtering ("PARMS") using an additional plasma source or the high pulse power magnetron sputtering ("HiPIMS" or "HPPMS") can be applied therefore. The present paper gives results of film properties of optical materials obtained with these ionized magnetron sputtering techniques and discusses potentials of the techniques for the use with precision optics.

The production of advanced optical coatings with complex spectral characteristics and high performance is directly dependent on the stability of the deposition process and on the accuracy of the monitoring system employed for controlling the thickness of the constituent single layers. The present contribution is concentrated on the current state in deposition control and manufacturing of coatings with improved precision. As major topics the simulation of deposition processes, modern monitoring concepts, and the handling of errors occurring during the deposition process will be discussed. For illustration of some recent developments, results on the deposition of rugate filters on the basis of an ion beam sputtering process will be presented.

In the case of plasma ion assisted deposition (PIAD) processes either quartz crystal monitoring or optical monitoring are commonly applied to control thickness of the layers. For several oxide layer materials the final stoichiometry of the deposited film is extremely sensitive to the oxygen gas inlet during the deposition process. It is well known, that under these circumstances, variations in the reaction gas flow or in deposition rates may cause unwanted variations of the stoichiometry of the coating. Finally this results in film inhomogeneities and increased absorption losses, which cannot be identified early enough and reliably by in-situ transmission spectroscopy alone. For this reason, the correlation between optical performance of the coating and emission spectra of the APS-plasma measured by a separate analyzer has been investigated. The synchronization in recording in-situ transmission spectra and plasma emission spectra was achieved by developing a common trigger unit for both spectrum analyzers. From the correlation between spectrophotometry and emission spectroscopy, we expect an earlier and more reliable assignment of absorption losses and inhomogeneities to instabilities in the process parameters of the deposition process.

In many coating chambers substrates are moved by simple or planetary rotary motion systems. Isaac Newton already taught that an object in uniform motion tends to stay in uniform motion unless acted upon by a net external force. To move a substrate on a rotary trajectory, centripetal and gravitational forces must act upon the substrate. The substrate must be somehow confined. Confinement options range from firm attachment to a fixture to loose placement in a pocket. Depending on the rotary motion pattern, a loosely held substrate may slide once against a confinement boundary and then stay, or may constantly slide around. 'Rattling around' may be undesirable as it could lead to edge destruction, debris formation, precession of the substrate, and other adverse effects. Firm attachment is advantageous in most cases, but often adds process complexity. We examine the forces present on substrates in typical rotary motion systems and discuss the implications of different confinement methods.

The substrate temperature is one of the key parameters, which determines the optical properties of deposited dielectric coatings. Depending on the employed material and application, the accurate knowledge of the substrate temperature is crucial for the system performance. Currently, the heating process inside the evacuated deposition plant is usually performed by radiation sources. The temperature of the substrates is governed be their emission and absorption characteristics and in minor degree, by heat conduction to the substrate holders. Pyrometric methods and temperature sensors are commonly used to measure the temperature close to the substrates. In any case, the measured temperature can deviate extremely from the real substrate temperature. In particular, if materials with a high transmittance in the IR range are used, the heating process can be controlled only with a large error by the conventional methods. In this contribution, an adapted method using optical characterisation of the substrate is presented to determine precisely the substrate temperature. In the described method, the optical transmittance of the components is measured and the absorption characteristic in the VUV and visible spectral range is used to evaluate the current substrate temperature.

For the production of high performance multilayer systems optical monitoring is essential. Substantial progress was achieved by the introduction of direct monitoring on the rotating substrate holder. It is a complex task to develop a stable monitoring strategy for multilayers with a large number of layers and irregular thicknesses. The verification and improvement requires the feedback of more or less numerous real coating runs. This expensive and time consuming trial and error method can be reduced significantly by computer simulation of coating runs. A new software tool which simulates the coating process with monochromatic optical monitoring is introduced. Process instabilities are described by systematic and random errors of the deposition rate, refractive indices, etc. For the simulation of the monitoring curve real monochromatic bandwidth, signal noise, measurement frequency, etc. are taken into account. A UV-IR cut filter and a single notch filter design were simulated with virtual deposition runs. In both cases the simulation results were confirmed by real coating processes.

Over the past decade, tremendous strides have been made in the design, manufacture and measurement of optical thin film filters. Driven in part from the challenging demands of fiber optic communication (telecom) filters, the manufacture of optical coatings has advanced significantly through improved optical monitoring technologies and algorithms; improved deposition technologies; and, very importantly, the ability to fully automate all aspects of the coating process. This improvement in optical coating technology has since been applied to filters used in other diverse fields ranging from bio-medical instrumentation to sensors to astronomy. In this paper, advanced optical thin film filters will be described along with their applications, both in telecom and spectroscopic fields.

For Notch Filters, Rugate designs with a small index contrast and apodisation are well known in the literature. The required deposition of gradient index layers or so called flip flop structures is very complicated and difficult to manufacture. Higher order H/L stacks of coating materials with high index contrast result in very thick layer stacks. In our approach we replace the second refractive index by equivalent layers consisting of H/L materials with high index contrast. This leads to a combination of thick (>100nm) and very thin layers. Stable coating processes with dense layers are strict requirements. Another challenge is the accurate thickness control of very thin layers in the nanometer range. Single notch filters were produced with PIAD and broad-band optical monitoring. The most challenging filters were demonstrated with magnetron sputtering and monochromatic optical monitoring. Some outstanding results of single and multiple notch filter coatings will be presented.

Magnetron sputtering of a silicon target in a time-variant mixture of the reactive gases oxygen and nitrogen allows the deposition of optical multilayer and gradient layer systems of silicon oxinitride at one stationary sputtering station. In this paper the processes within the sputter discharge and the properties of the growing film during the change of the reactive gas composition are investigated using optical in-situ monitoring, optical plasma emission spectroscopy and plasma impedance monitoring. A time delay between the change to the reactive gas composition and the resulting change to the film composition was observed. The time delay is longer for the transition from oxide to nitride deposition then vice versa. This asymmetry is attributed to the different affinity of nitrogen and oxygen to the silicon target. Examples of deposited antireflective coatings as well as rugate filters based on silicon oxinitride multilayer and gradient layer designs are given.

The term photocatalysis is used to describe a photon-driven catalytic process. Titanium dioxide is a well-known photocatalyst in such fields as self-cleaning material and anti-microbial effects. Besides these photocatalytic applications, TiO₂ is a widely-used high index material for optical thin films. In the present investigation, the photocatalytic activity of transparent TiO₂ thin films was optimized to achieve multifunctional high precision optical coatings. The films have been deposited by ion assisted deposition (IAD), applying a Leybold APS plasma source as well as a Denton CC-105 ion source. The cause-and-effect chain between the use of different parameters in the IAD process and optical properties of the TiO₂ layers as well as their photocatalytic activities are described. As test reaction for the determination of the photocatalytic properties, the degradation of methylene blue (MB) was chosen. The used setup based on a high precision two-path laser measurement system was developed by the LZH in order to determine the kinetic performance of TiO₂ catalysts under well-defined UV illumination conditions. Photonic efficiencies of the TiO₂ thin films were calculated from the obtained data. Additionally, crystal structure analysis has been investigated for the identification of anatase and rutile modifications. The comparison of the results shows that ion assisted deposition is an appropriate technology for the preparation of photocatalytic active thin films for optical applications.

ArF lithography technology requires minimization of optical losses due to scattering and absorption. Consequently, it is necessary to optimize the coating process of metal fluorides. The properties of metal fluoride thin films are mainly affected by the deposition methods, their parameters (temperature and deposition rate) and the vacuum conditions. A substrate temperature of more than 300°C is a condition for high density and low water content of metal fluorides. Therefore, a substrate temperature of 150°C results in inhomogeneous films with high water content. Until now, the best results were achieved by boat evaporation. This paper will demonstrate that most of the common metal fluorides like MgF₂, AlF₃, and even LaF₃ can be deposited by electron beam evaporation. In comparison to other deposition methods, the prepared thin films have the lowest absorption in the VUV spectral range. Furthermore, metal fluoride thin films were prepared by ion assistance. It will be demonstrated, that they have less water content, high packing density, and low absorption in the VUV spectral range. In this study, single layers of LaF₃ and AlF₃ and antireflection coatings were prepared by electron beam evaporation with and without ion-assistance. The mechanical, structural, and optical properties were examined and discussed.

The process of fabricating optical surfaces has remained relatively unchanged for hundreds of years and only within the last 10-20 years have significant improvements been made to the basic techniques of manual polishing. Various deterministic grinding, etching, and polishing machines are now available that can generate free-form optical surfaces by sub-aperture removal of surface material. This presentation will concentrate on a new technique for deterministic surface correction that is achieved using selective deposition of an index matched material simultaneously over the entire surface of the optic. The technique uses a multi-aperture mask to selectively occlude the plume from a physical vapour deposition system. The mask design has two functions; firstly to remove the inherent variation in the plume itself; and secondly, to create the required spatially varying layer to correct or form the final optical shape. This ability to correct the entire surface of the optic simultaneously has the considerable advantage that the corrections are achieved in a very short space of time and deposition times of 100-300 seconds are typical. A further advantage of this technique is that the surface roughness does not seem to be affected by the deposition process, and so the surface quality of the optic is maintained throughout the correction process. The technique has been successfully applied to both transmissive and reflective optics and has achieved uniformities of λ/1000 rms. During the talk I will present our latest results and progress towards selective etching, full edge correction, and spatially varying thin-film filter deposition.

Highly transparent thin films of indium tin oxide are important for different kinds of optical and electrical applications. So far, deposition of these materials has been limited to high temperature processes. This study describes a plasma ion-assisted evaporation process with substrate temperatures below 100°C and correlates the structural and electrical properties of the coatings with the process parameters. The influence of gas-mixture, mean ion energy and temperature has been investigated by four-point-measurement, atomic force microscopy, scanning electron microscopy and x-ray spectroscopy. The coatings exhibit mean extinction coefficients of 7•10^-3 in the VIS range and specific resistivities in the range of 4.0 μΩm.

Interference filters for spectroscopic purposes or sensor applications are characterized by strictly specified spectral blocking and transmitting regions with intermediate steep edges. These steep edges must be positioned within nanometer accuracy while the coating may consist of more than one hundred non-quarterwave layers. Though modern ion assisted deposition processes in conjunction with quartz crystal control are well suited for the production of complex filters, an optical monitoring device seems to be necessary to fulfill the demanding spectral requirements. Broad band optical monitoring (BBM) directly on the calotte has been employed to control the production of this type of band stop filters. For a large number of also different types of these coatings the BBM-technique demonstrated its capability to improve the reliability and flexibility in industrial production. Within a stable well-characterized deposition process error self-compensation effects allow for a fast realization of various designs within specified tolerances. Nevertheless, optical broad band monitoring could not be applied to all types of these steep edge filters because error propagation leads to unreachable solutions of the thickness tracing algorithm for specific cases. The given examples of complex steep filters and the corresponding post analysis of stored online spectra as well as the simulation of the monitoring process reveal the influence of the design itself to this occurrence. A suggestion for an identification of critical thickness values within the layer sequence is discussed and solutions to the problems are presented.

Hydrophobic coatings enable the manufacture of easy-to-clean surfaces having dust- and water-repellent properties. In this work, a hydrophobic coating is deposited as a top layer on an antireflective (AR) multilayer system comprising a MgF₂ upper layer to produce low reflectance optical surfaces at a normal incident angle in the visible spectrum with dust- and water-repellent properties for applications in precision optics. We report on the preparation and characterization of the optical properties of hydrophobic coatings deposited using a vacuum evaporation process and a commercially available water repellent substance. By means of a grazing incidence X-ray reflectometer it is shown that the hydrophobic coating can be considered, from an optical point of view, as two adjacent thin layers having specific thicknesses and densities. In fact, the hydrophobic layer is one monolayer comprising molecular chains with anchoring groups responsible for the chemical bond with the substrate material and functional groups responsible for the water- and oil-repellent properties. Optical constants are determined using a spectroscopic ellipsometer and are taken into account in the final multilayer system design. High performance AR coatings having an average reflectance of 0.14% at 7° incident angle in the 400-680nm spectral range together with a pleasing purple-red reflex color are produced. Coated lenses exhibit an excellent abrasion resistance, environmental stability, resistance to cleaning agents, homogeneity and water repellence with contact angles against water higher than 110°.

An overview of methods for experimental determination of thin film optical constants is given, with an emphasis on recent advances in non conventional optical techniques. The generalized ellipsometry, the photothermal deflection spectroscopy (PDS) and the surface plasmon resonance (SPR) spectroscopy are more sophisticated and versatile tools, compared to traditional spectrophotometry and ellipsometry. The generalised ellipsometry in terms of Jones or Mueller matrix coefficients provides a more detailed model of the layered structure: material anisotropy, layer roughness, etc. The PDS may yield the accuracy of the direct absorption measurement unavailable with other approaches. The SPR phenomenon may be used for characterisation of ultra thin films, even having a complex spatial distribution, as well as to retrieve information on the refractive index depth distribution in the near-to-surface film zone. The advantages and drawbacks of these methods of thin film optical constants characterization are discussed. The complementary nature of various measurements allows deeper understanding of layered structures formation by non destructive optical methods. The examples of application of these techniques for characterization of single films and multilayers are given.

In the aim of describing the thermo-mechanical behaviour of a thin-film filter, simplified models have been studied. An easy way is to determine the evolution of the optical properties of each layer composing the stack, and thus to derive the features change at the component level. Therefore, the knowledge of physical parameters describing each material, such as the coefficient of thermal expansion, the thermo-optic coefficient, the Poisson's ratio and the elasto-optic coefficients, is required. The main challenge is to evaluate these parameters at a single layer level. We propose here a new optical method, based on the analysis of the thermal behaviour of two dedicated Fabry-Perot (FP) structures including a thin disk of the material under study. In parallel, we show through modelling, that we can determine the physical properties of this material with a high accuracy, only by measuring the shift of FP resonance wavelengths. However, we have to take into account the mechanical deformation of the Fabry-Perot structures induced by the thin-film deposition process as well as its evolution with the temperature change (thermal stresses). In this goal, we carried out an accurate study of the thermo-mechanical behaviour of our interferometric structures by using a Finite Element Method.

Dense-wavelength-division-multiplexing (DWDM) filter is a very sensitive component in wavelength shift. The temperature shift of central wavelength (TSCW) of filter is depended on the mechanical properties of the stress. In this paper, a modified Stoney's equation was applied to analyze the thermal stress of DWDM filters for the reason of the thickness ratio (thin film thickness/substrate thickness) larger than 1%. The phase-shift interferometer and TSCW were applied to measure and achieve the coefficient of thermal expansion (CTE), biaxial modulus, temperature optical coefficient, stress optical coefficient, and Poisson ratio of DWDM filter. Based on this method, we can obtain the CTE of DWDM filter 0.87pm/ °C ,the biaxial modulus 41 GPa, Poisson ratio 0.22, temperature optical coefficient 1.4×10^-5 / °C, and stress optical coefficients -1.9×10^-12 /Pa. To achieve zero TSCW for a DWDM filter, the CTE of the substrate should be 10.36ppm/ °C.

In the field of scanning white light interferometry (SWLI), it is well known that films of optical thickness in excess of the coherence length may be measured by simply taking advantage of the fact that such films exhibit interference maxima corresponding to each interface. In fact for the majority of such 'thick' films the determined thickness has a DC error arising from the spectral phase-change on reflection at the two interfaces. For thinner films, the interference maxima coalesce and it was for this regime that the HCF (helical complex field) was previously introduced to allow thin film extraction. This work has now been significantly extended with a demonstrated capability to extract film interfaces with a lateral (XY) resolution of 1.25μm and a (Z) surface rms noise of ~0.75A (angstrom). It is also capable of covering both the thin and thick film regimes (from ~50nm to several microns, both limits being material dependant). Results are presented showing the performance of this approach, these include 'micro-scratches' that are apparent in the thickness of the deposited layers as well as substrate/film and film/air interfaces. These are compared to the original 'surface' as determined by SWLI and by AFM surface measurements. Additionally a brief comparison is made between film thickness determination using this approach, spectrophotometry, ellipsometry and stylus profilometry.

Light scattering is a current tool for characterization of defects in optical interferential coatings. However, this tool is not fully efficient for multilayer component. Indeed, in this case, the scattered light from multilayers originates from several interface roughnesses that cannot be separated a priori. In this paper, a technique which can isolate a single interface embedded within a stack is presented. It is based on destructive interferences between the polarization modes of the angular scattering. These interferences can be tuned in a selective way that allows the extraction of light issued from a specific scattering interface.

A summary of the research performed on the optical characterization of Sc and of several lanthanides from the visible to the soft x-rays is presented. The low absorption of these materials mainly below the O_2,3 edge (L_2,3 edge for Sc) turns them promising materials for the realization of multilayer mirrors in a spectral range in which most materials in nature absorb strongly. Thin-film samples with several thicknesses of the target material were deposited by evaporation over thin-film substrates in UHV, and their transmittance was measured in situ. A wide spectral range of direct characterization, along with extrapolations to longer and shorter wavelengths either using literature data (when available) or model predictions, enabled the development of consistent optical constants over the whole spectrum. An assortment of consistency sum rules has been used, and it was found that each of them highlights a given spectral range, which may help evaluate the consistency of each part of the combined spectrum.

The latest generation of 193nm immersion lithography optics, with a numerical aperture (NA) of 1.35 and ultra pure water as immersion fluid serves the 45nm node on the ITRS roadmap. The potential solutions for the next step, the 32nm node, as presented in December 2007 by the ITRS are: 193nm double patterning / exposure, 193nm with 2^nd generation fluid and EUVL. The performance of such next generation lithography optics is increasingly driven by the coating performance. For 193nm the performance of the antireflection and high reflection coatings is driven by the increasing NA, which requires the control of polarisation effects and transmission uniformity over light incidence angles. For EUV only high reflection coatings are needed and the NA is comparatively small. But the performance is limited by higher absorption and lower refractive index contrasts of the applicable coating materials at 13.5nm with respect to 193nm. In this talk we discuss and compare the different requirements and challenges in coating material, design, process, lifetime and accuracy for next generation lithography optics.

High reflective coatings for 193nm wavelength and 45° incidence were developed which combines the advantages of all-oxide and all-fluorides layer stacks. Using plasma-assisted evaporation very smooth and dense Al₂O₃/ SiO₂ multilayers showing small light scatter were deposited onto fused silica substrates. In the same coating process followed metal fluoride stacks, which could reduce the resulting coating absorption at 193nm. The non-polarized reflectance of combined stacks at 193nm is R>98.5% at 45° and R>98.0% for an angle range of 42°-48°. As the number of fluoride layers could be drastically reduced compared to all-fluoride coatings any formation of micro-cracks could be avoided. The stress of the oxide/fluoride stacks was less than 40MPa.

The demand for enhanced optical resolution in order to structure and observe ever smaller details has pushed optics development in recent years. There is increasing interest in optical components for the extreme ultraviolet (EUV) spectral region mainly as a result of the production of more powerful electronic circuits with the aid of projection lithography. Due to absorption at wavelengths below 100 nm the penetration depth of EUV radiation into matter is only a few nano-meters. Hence, reflective optics must be used for imaging and light collection such as EUV multilayer mirrors which consist of alternating thin films with different refractive indices. This basic idea can be compared to the classic, high reflective λ/4 systems: the constructive interference of all beams reflected at the film interfaces. At Fraunhofer IOF Jena multilayer optics development cover the full range between the soft X-rays around 2 nm wave-length and the vacuum ultraviolet. However, the paper will focus on multilayer optics for EUV lithography applications at 13.5 nm. Besides the development of high-reflective multilayers with enhanced thermal and radiation stability using interface engineering and optimized capping layers collector and imaging optics for diverse applications in the EUV spectral range have been realized. The deposition of EUV collector mirrors for high-power laser produced plasma (LPP) sources is discussed. The paper summarizes recent progress and the present knowledge in preparation and characterization of multilayer optics for the EUV spectral range with regard to maximum optical performance, minimization of structure imperfections, reduc-tion of residual stresses as well as enhanced thermal and radiation stability.

Non-periodic multilayer coatings offer engineer great flexibility to achieve tailored spectral performance in EUV, soft X-ray and X-ray region. We have developed a variety of non-periodic multilayer mirrors for use as optical key components for polarization-sensitive studies, Kirkpatrick-Baez microscope, Earth's magnetosphere observation and reflection of sub-femtosecond pulses. To find optimal distribution of layer thicknesses for a given spectral response, several numerical algorithms, such as simplex, simulated annealing, genetic and Levenberg Marquardt, have been explored to solve the reverse optimization problems. The designed non-periodic multilayers were prepared by use of a direct current magnetron sputtering system and characterized by grazing incidence x-ray reflectometry analysis. The synchrotron measurements of these samples were performed at the National Synchrotron Radiation Laboratory, China and at the beamline UE56/1-PGM-1 at BESSY II Berlin, Germany. This paper covers our recent results of design and fabrication of non-periodic multilayer coatings. And the mirror performance and limitations were also briefly reviewed.

Phase controlled optical thin films on solid cube corner retroreflectors have been shown to successfully maintain the polarization state of the incident light. This paper considers the theoretical basis for this effect when only two of the three total internal reflecting faces of the cube corner have coatings with zero phase retardation and when the incident light is monochromatic and S or P polarized. Such polarization preserving retroreflectors are highly useful and are integral components in advanced heterodyne displacement measuring interferometer systems.

A lightweight and compact spectrometer with spectral resolution in the order of 0.1 nm, in a spectral range from UV to NIR, can be implemented using a spectral pre-selection technique at the spectrometer entrance, through transmission variable filters. Such filters, based on thin-film optical coatings, have either a transmission peak or a transmission edge that moves along one direction of the filter surface. Depending on the spectrometer design, different configurations of the pre-selection device are possible. The operating spectral range (240-800 nm) is divided in a number of sub-ranges and in each of them the filter transmission peak, or edge, is displaced from the minimum to the maximum wavelength over a distance of few mm. Two cases are considered: a configuration with both a narrow-band transmission filter and a band-pass filter having a linear spatial variation and a configuration with an edge filter having a non-linear spatial variation. To obtain the required spatial profile of filter performance, a graded coating is deposited on a fused silica substrate, by r.f. sputtering with a moving mask. Details on filter requirements and fabrication technology are reported.

As improvements to the optical design of spectrometer and radiometer instruments evolve with advances in detector sensitivity, use of focal plane detector arrays and innovations in adaptive optics for large high altitude telescopes, interest in mid-infrared astronomy and remote sensing applications have been areas of progressive research in recent years. This research has promoted a number of developments in infrared coating performance, particularly by placing increased demands on the spectral imaging requirements of filters to precisely isolate radiation between discrete wavebands and improve photometric accuracy. The spectral design and construction of multilayer filters to accommodate these developments has subsequently been an area of challenging thin-film research, to achieve high spectral positioning accuracy, environmental durability and aging stability at cryogenic temperatures, whilst maximizing the far-infrared performance. In this paper we examine the design and fabrication of interference filters in instruments that utilize the mid-infrared N-band (6-15 μm) and Q-band (16-28 μm) atmospheric windows, together with a rationale for the selection of materials, deposition process, spectral measurements and assessment of environmental durability performance.

The 1600 mirrors required for the National Ignition Facility (NIF) are now coated with the last optics currently being installed. The combined surface area of the NIF mirrors is almost 450 square meters, roughly 3.4 times greater than the surface area of the two Keck primary mirrors. Additionally, the power handling specification of NIF mirrors is 19 orders of magnitude greater than that of the Keck mirrors. The NIF laser will be at least 40× greater energy than the previous LLNL fusion laser called NOVA. To manufacture these mirrors, a number of new technologies (electrolytic in-situ dressing, ion figuring, source stabilization) were used that were not available for previous fusion laser optics. Post deposition technologies designed to increase laser resistance (off-line laser conditioning, solarization, air knives) have also been utilized. This paper summarizes the differences in technologies used to manufacture NIF mirrors from those used for previous fusion lasers and examines potential future technologies that would enable higher fluence operations and extend lifetimes.

We demonstrate numerically and experimentally two types of dispersive mirrors with the controlled reflectivity and dispersion in a 1.5-octave bandwidth in wavelength ranges of 300-900 nm and 400-1200 nm. The measurement of the dispersion in a wavelength range of 300-1200 nm was performed. These types of dispersive mirrors allow one to correct the phases of the corresponding spectra, supporting sub-2-fs and sub-3-fs pulses, respectively.

We describe in this paper a model to link laser damage initiators properties (nature, size distribution, density) to measured Laser Induced Damage Threshold (LIDT). It is based on calculation of light absorption in nanoabsorbers and subsequent heating, coupled to laser damage statistics in order to obtain the laser damage probability as a function of laser fluence. Applications to the case of optical coatings are then presented. We study the influence of laser irradiation parameters and coatings properties on LIDT measurements. By coupling this multiscale study to our model, we show that information on the initiating defects properties and the physical damage mechanisms involved can be obtained: discrimination between different defects, estimation of densities, size and nature of defects, evolution of the defects under multiple irradiation. Implication of this approach for physical understanding and metrology applications are discussed.

The development of high power laser for large instruments such as LMJ and NIF, as well as the use of smaller optical structures with high densities of energy lead to consider laser induce damage threshold (LIDT) as a critical criterion in optical components development. Furthermore in the same time some applications need an increase of the lifetime of the laser source (up to 109 shots for spatial applications). In this context to improve optical components numerous studies are undertaken to determine the origin of laser damage process. Through these studies, it is now commonly admitted that the first stage of the laser damage process in the nanosecond regime is caused by localized defects included in the material. In order to determine the laser damage threshold, it is necessary to perform a statistical study of damage on materials. This destructive technique beyond the determination of damage threshold allows to determine the density of precursor centers and to discriminate different kinds of precursors by using adapted beam sizes. However the nature and therefore the origin of the defects remain unknown. In order to get information on this nature, non destructive tools have to be involved. Indeed on one hand photothermal microscopy permits to make measurement of the local absorption under irradiation, on the other hand, photoluminescence cartography and spectroscopy gives information on material composition. The coupling of the different techniques on a laser damage test set-up optimizes the chance to have a complete signature of precursor center and information about the mechanism of damage process. Furthermore, nondestructive diagnostic under mutilple irradiations permit to study "fatigue" and conditioning process.

Narrow bandpass filters have historically been designs of quarter waves at the passband wavelength, and have been monitored at the turning points using the passband wavelength. By direct monitoring at the passband wavelength, errors have been shown to be primarily self compensated, and have allowed much better performance than could otherwise be expected. The turning points are difficult to detect precisely and accurately because the change in transmittance with thickness becomes zero at the desired termination point. By proper design with non-quarter-wave layers, essentially the same spectral performance can be achieved by layer terminations that are far enough from turning points to be significantly more sensitive termination points. The design approach is to maintain the optical thickness of the reflector layer pairs at one half-wave of the passband wavelength, but change the ratio of the optical thicknesses of the high and low index layers. These can be adjusted enough so that the thicker layers contain two turning points and the last turning point in the layer can be more accurately and precisely determined. The error compensation benefit from the historic method should be maintained. This leads to potentially improved control during deposition and monitoring of narrow bandpass filters.

Due to the gradient of the phase shift as the wavelength in the reflection and transmission, the optical thin films coatings will present the spatial dispersion effect. The new kinds of super-prism thin film devices can be realized by well design interference effect inside of multilayer films to get the super-dispersion. The positive and negative spatial dispersion are existed in side of coatings, and is very sensitive to the angle of incident and wavelength. The analysis methods and the different kinds of spatial dispersion thin film filter devices and tunable spatial dispersion filter devices are presented in the paper.

A resonant grating filter can be basically described as a sub-wavelength grating inscribed on a a planar waveguide made of dielectric thin film layers. The reflectivity of such a structure presents some peaks versus the wavelength that are generated by the coupling and coupling out of different modes of the waveguide. These peaks can be tailored in order to create free-space narrow bandpass inverse (notch) filters, with a very sharp spectral response (typically a spectral bandwidth below 0.5 reflectance nm for a component working at 1550nm). We show an experimental demonstration of a high performances resonant grating filter working in reflectance under a given incidence and wavelength. This filter presents simultaneously a good angular tolerance and polarization independence with a full width at half maximum about 0.4nm. The dielectric stack reflectance configuration is chosen so that the coupling conditions for two TE reflectance guided modes are simultaneously satisfied. Moreover, the grating cell presents a complex structure of four holes with different diameters, optimized for increasing the angular tolerance of the filter while maintaining a narrow spectral width for any polarization. Comparisons with theoretical calculations are provided.

Spirooxazine (SO) photochromic molecules were trapped in sol-gel matrices. In order to increase the colourability and improve mechanical properties of sol-gel photochromic films, we present an original strategy in which SO photochromic molecules were dispersed in mesoporous organized films using the impregnation technique. Well-ordered organosilicate mesoporous coatings with the 3D-hexagonal symmetry were prepared by the sol-gel technique. These robust mesoporous films, which contain high amounts of hydrophobic methyl groups at the pore surface, offer optimized environments for photochromic dyes dispersed by impregnation technique. After impregnation by a spirooxazine solution, the photochromic response is only slightly slower when compared with mesostructured or soft sol-gel matrices, showing that mesoporous organized hybrid matrix are good host for photochromic dyes. Moreover, the molecular loading in films is easily adjustable in a large range using multi-impregnation procedure and increasing the film thickness leading to coatings for optical switching devices.

We present the characterization of silicon oxide (SiO_x) and silicon nitride (SiN_x) films deposited by inductively coupled plasma chemical vapour deposition (ICP-CVD) at low temperature (< 100°C). A tunable optical Fabry- Perot (FP) -filter operating at a wavelength around 1.5μm is realized. It is hybridly assembled with two dielectric distributed Bragg reflectors (DBR). One of the DBR- mirrors is intentionally curved using the intrinsic stress inside the films. Our aim is the development of a tunable surface micromachined VCSEL with a curved dielectric mirror. Therefore ICP-CVD with a low deposition temperature is used for SiO_x and SiN_x films. As a first step the realization of a tunable bulk- mircomachined optical FP- filter is presented. The refractive index, deposition rate, stress and etching rate in buffered hydrofluoric acid (BHF) of thin dielectric films (<500 nm) in dependence on deposition temperature and on gas flow ratio are investigated. The knowledge of the deposition characteristics of the dielectric films is used to realize DBRs with a given curvature that are applied to electrothermally actuated, optical tunable FP- filters. The presented filter has a free spectral range of 29 nm, an insertion loss of 10 dB and a full width half maximum of 0.16 nm.

Aluminium nitride films, 0.8-1.8 μm thick, have been deposited by reactive, magnetron sputtring of aluminium in an argon-nitrogen atmosphere. The sputtered films exhibit a Reststrahlen band in the wavelength range 11-16 μm. We have investigated the possibilities to use different substrate materials and dielectric coatings to extend this interval to the entire upper thermal window 8-13 μm and a secondary interference maximum in the 3-5 μm range, i.e. the lower thermal window. Our results indicate a potential for the use of AlN-films in applications that benefit from wavelength selective emittance, e.g. IR signature control and frost prevention.

The optical and structural properties of Nb_xSi_yO composite films prepared by metallic co-sputtering process have been investigated. Compositional modulation of Nb_xSi_yO mixed films is controlled by changing the relative sputtering rates of metallic niobium and silicon. The deposited intermediate index films have been characterized by spectrophotometry. And the dependence of the refractive index on composition is examined and compared with different mixing models. A comparison is made between the mechanical properties of the discrete multilayer and the gradient-index filter. It is demonstrated that the gradient structure exhibits a higher mechanical strength and integrity. Moreover, two typical gradient-index filters have been designed and realized using Nb_xSi_yO composites. Their spectrum performances and microstructures are also presented.

This paper describes an experimental arrangement to determine phase retardations with changing signs around zero degree. In the experiment the phase retardation is caused by reflection from a non-periodic multilayer thin film reflector. A prism retarder is introduced in a common polarimetric measurement to act as a compensator in order to enable the measurement around zero degree phase retardation. Phase retardation within plus/minus a few degrees is measured in a broad spectral range using a fiber coupled spectrometer.

During the interaction with a coating, a phase shift is introduced on the light. In general this phase shift is different for S and P-polarized light. This means that the state of polarization may be changed during the interaction with the coating. Working with laser beams it is common to polarize the light parallel or orthogonal to the plane of incidence. In this case phase retardation does not occur. This explains why most people forget about the phase performance in their daily work. On the other hand, it is possible to utilize the phase retardation. For example it is possible to design a coating transforming a linearly polarized beam into a circularly polarized beam, and it is possible to make the phase retardation independent of the wavelength in a certain wavelength range. Equations and a design technique are presented for first and second order optimization of the phase retardation on reflection or transmission of light from optical coatings. The optimization is performed by alternating optimization on the phase characteristics and the phase targets for S and P-polarized light. Examples of the design of laser mirrors with zero retardation and quarter wave retardation are presented.

A high refractive index dielectric layer of thickness λ/4 on the backside of a metal layer can reduce the absorption losses of metallic beamsplitters considerably. This was published by H. Pohlack in 1953. The practical importance of this knowledge may even be greater nowadays, as the availability of sputtering techniques makes the combination of metallic and dielectric layers within an optical coating much easier. In this contribution it will be shown, that the inclusion of dielectric layers into a metallic beamsplitter can possibly have further benefit. For some applications, where achromatic transmission and/or reflectance are needed, an additional dielectric layer can enhance the performance of a metallic beamsplitter. As an example the coating of a beamsplitter cube will be shown. The projected application of this cube demands a high reflection and only a low transmission over a spectral range from 400 nm to 800 nm. Using a metallic beamsplitter coating enhanced by a high refractive index dielectric layer it is possible to fulfil this demand with a comparably simple coating and at the same time to obtain a constant transmission of about 5% over a large spectral range.

In this work, physical and optical properties of ZnS films grown at different evaporation conditions have been studied. ZnS 3000 nm thick films have been deposited on Ge substrates at 200°C, 120°C and without substrate heating. In addition, evaporation rates of 4, 2 and 1 nm/s have been considered. The structural and morphological properties of the films have been analysed by XRD and AFM, respectively and the refractive index in the 2.4-11.5 microns range has been determined from transmittance spectra through reverse synthesis. From this analysis, the most suitable evaporation conditions for ZnS thin films deposition have been defined in terms of film properties and intended applications on thermal IR multilayer coatings. Afterwards, adhesion properties of ZnS films deposited under the optimised conditions have been analysed. ZnS films deposited at 120°C and 4 nm/s peeled off when subjected to MIL-F-48616 standard surface durability testing. The use of a MgO bonding layer to enhance the ZnS film adherence to the substrate has been proposed and its effect on the ZnS film properties has been studied. Finally, the mechanical stability of the ZnS coating under MIL-F-48616 standard testing has been confirmed for films grown onto MgO coated substrates.

Increased performance of optical coatings with ion assist during electron beam evaporator deposition (IAD) has been well established. Over the years, the gridless Mark II end-Hall ion source has been widely used to produce IAD optical coatings (antireflective coatings, dielectric filters and mirrors) on unheated substrates with low losses, high precision and high environmental stability. We report on the performance of a next generation end- Hall ion source (Mark II⁺) in an optical coating production environment in replacement of the earlier Mark II. The Mark II⁺ was thoroughly re-designed with two major effects: (1) ion generation was enhanced resulting in a significant increase in ion current density of about 20%, and (2) serviceability was greatly improved by incorporating a removable and replaceable anode sub-assembly. The question arises as to how the enhanced output of the Mark II⁺ might affect the properties of optical coatings when replacing a Mark II source in established IAD coating processes. To answer this question, the spatial distribution of optical films parameters of high and low index oxide materials were analyzed when using either ion source. The coating process and results produced with the Mark II⁺ are basically compatible those of the Mark II, with slight changes in the spatial distribution of refractive index and film thickness. Given the higher ion flux output of the improved Mark II⁺, the ion source parameters for minimum absorption can be adjusted to lower, more energy saving levels. Thus the Mark II⁺ is a tool to achieve comparable or marginally better results for optical coatings with higher efficiency.

In the present paper we focus on the fabrication of rib waveguides being able to work in the large infrared window [6-20μm], compatible with the Darwin mission requirements. The rib waveguides to be realized are based on etched thick films of telluride materials deposited on telluride glass. The choice of the Te₇₅Ge₁₅Ga₁₀ material as the substrate is justified by its excellent transmission in the infrared region and its thermal stability. Films of the ternary system made of Te, Ge and Ga were investigated as the core layer and the superstrate. Details are provided on the film deposition and etching technologies: (i) Te-Ge-Ga films are prepared by co-thermal evaporation from the pure elements Te, Ge and Ga; (ii) the geometry of the as-obtained films is modified by reactive ion etching under an atmosphere of CHF₃ + O₂ or CH₄ + H₂. First results concerning Te-Ge binary films are particularly interesting.

Nonlinear refraction has been for the first time studied in silicon carbide nanocrystal films synthesized by new technique of direct carbide and silicon ion deposition with ion energy of 100eV and low substrate temperature from 900°C to 1150°C. The films were shown to exhibit large optical nonlinear cubic susceptibility χ⁽³⁾ ≅ 10^-6 esu (λ=1064nm and λ=532nm, τ_и = 10ns).

Aluminium-doped zinc oxide films with 91% transmittance in the visible range and electrical resistivity of the order of 10^-3 Ωcm were fabricated by radio frequency magnetron sputtering in Ar atmosphere starting from a target of ZnO mixed with 2% wt Al₂O₃. A systematic study of the deposition conditions such as substrate temperature, working gas pressure, radio frequency power, magnetron strength, target to substrate distance, etc., was performed when searching for improved electrical and optical performances of the films. Several deposition conditions govern the film characteristics, so that films with same good optical and electrical properties can be obtained by opportunely combining different deposition parameters.

Residual absorption in optical thin films due to impurities or defects causes thermal lens formation upon high power DUV laser irradiation. Furthermore, it may be one reason for functional degradation during prolonged laser irradiation. Pulsed ArF laser induced fluorescence (LIF) and direct absorption measurements (LID technique) are applied to investigate high reflecting coatings made from LaF₃, MgF₂ and AlF₃ with respect to the influence of different raw materials and deposition temperatures. LIF measurements reveal emission bands that are partially attributed to certain impurities or defects which either origin from the raw material or the coating process. In addition, LIF measurements of single MgF₂ and LaF₃ layers are performed to investigate different raw material qualities and coating processes. The experimental results show the potential of both techniques for sensitive accompanying of coating process development.

Giant nonlinear refraction has been experimentally observed in gold island films. The complex third-order nonlinear susceptibility χ⁽³⁾(ω;ω,-ω,ω) reaches a value of -8×10^-5 esu (λ = 532 nm, ι = 10 ns) and (+5×10^-7 + i0.3×10^-7) esu (λ = 800 nm, ι = 85 fs). The mechanism of nonlinearity of the refractive index can be associated with the resonance enhancement of the factor of the local optical field at the pump wavelength due to the excitation of surface plasmons, as well as with the contribution of the heating of conduction electrons in an ensemble of metal particles.

Metrology in the soft X-ray range has various applications ranging from instrumentation for solar astronomy to plasma experiments and EUV Lithography. The Physikalisch-Technische Bundesanstalt (PTB) with its laboratory at the electron storage ring BESSY II is a centre of soft X-ray radiometry and supports national and European research and development by carrying out high-accuracy at-wavelength measurements. The absolute detection efficiency of entire detection systems, diodes or cameras can be traced to SI units with a typical relative uncertainty of 0.5 % to 1 % using a cryogenic electrical substitution radiometer. For reflectometry on multilayer mirrors (MLMs) PTB operates a large reflectometer accommodating samples of up to 550 mm in diameter and 50 kg in weight, allowing sample alignment in 6 degrees of freedom. The relative measurement uncertainty for the spectral reflectance is typically in the range of 0.15 % and the long-term reproducibility in the range of 0.10 %. To investigate roughness, scatterometry is employed where scattered light around the specular beam is mapped using a calibrated CCD.

The astronomical instrument GROND (Gamma-Ray Burst Optical and Near-Infrared Detector), mounted on the 2.2m MPI/ESO telescope in La Silla (Chile) is an imaging system covering seven wavelength bands from the visual to the NIR spectral range (380-2400 nm). The instrument consists of more than 30 optical elements allowing the simultaneous observation of four wavelength bands in the visible spectral range (g, r, I, z) and three bands (J, K, H) in the near infrared. The deposition of high quality optical coatings on the optical elements of the system is one of the major challenges for the implementation of GROND. In order to tailor the instrument performance with respect to the required sensitivity parameters, a set of broad band anti reflection coatings and dichroic filter coatings on quartz, YAG and different fluoride compound lenses had to be optimized. The performance and deposition control of the optical coatings on plane and curved surfaces was evaluated with the aid of witness samples, which were deposited together with the real substrate. The global optical performance of the instrument can be determined combining the single components properties or by an overall measurement of the finalised instrument. In this contribution, a comparison of the measured performance and the operation characteristics predicted from the properties of the single elements is presented.

Metal island films show unique optical properties owing to the local surface plasmon resonance of islands free electrons. In the present study, the electric field assisted dissolution of clusters in metal island films is reported. Island films of Au, Ag, and Cu are deposited under different conditions by thermal evaporation and coated with thin dielectric layers. The samples are treated with the simultaneous application of an intense electric field and temperature, leading to the sample partial or total bleaching due to the dissolution of metal clusters in the films. Owing the facility of production of metal island films and the inexpensive technical requirements of the dissolution process, this approach suggests a novel path for the production of low-cost photonic structures.

We report on a hybrid monitoring strategy, which makes use of quartz crystal monitoring and broadband optical monitoring data in application to the deposition of chirped mirrors for the near infrared spectral region. We present a short description of the basic monitoring concept, the experimental setup, and the data elaboration facilities of the developed optical monitoring system OptiMon. Although being flexible enough to be implemented into different types of deposition system, we focus here on the application of our monitoring system for coating preparation with Advanced Plasma Source (APS) assisted electron beam evaporation. Chirped mirrors have been prepared using SiO₂ and Ta₂O₅ as low and high index materials, respectively. The layers are characterized by in-situ transmission spectroscopy, ex-situ transmission and reflection spectroscopy, and white light interferometry to determine the group delay dispersion GDD. Basing on characterization results, we demonstrate and discuss the relative benefits of the developed monitoring strategy.

Single wavelength (670 nm laser diode) optical monitoring of reflectance at 1 second intervals was used to observe the surface oxidation of Ni and Hafnium metal films in-situ in a low pressure oxygen atmosphere and also in a microwave plasma oxygen environment. After depositing thin metal films by sputtering in an oxygen-free environment, the observed reflectance quickly decreased when low pressure oxygen gas was introduced into the vacuum chamber and reached a stable value within a few seconds, after formation of a thin oxide layer. An additional rapid fall in reflectance and increase in oxide thickness was observed when a microwave plasma generator was used to produce an oxygen plasma containing atomic oxygen. Based on pre-determined optical properties of the metal and metal oxide films, the optical monitoring data was fitted to obtain the thickness of the metal oxide as a function of time. The fitting results showed that the exposure to low pressure oxygen forms an equilibrium thickness of less than 0.5 nm of NiO_x and 0.78 nm of HfO_x, while the oxygen microwave plasma treatment produces an equilibrium thickness of 1.5 nm for both NiO_x and HfO_x.