The first optical interference coatings were produced about 70 years ago. Since then, the optical coating industry has grown to serve a $2.1 billion market worldwide. There are three requirements to produce good multilayer optical interference coatings: 1. a good theoretical design; 2. at least two reliable coating materials; and 3. production processes which allow the deposition of these materials. A chart of historic milestones in the design of optical coatings was published before (An updated version of this chart is given below). In this paper we make an attempt to develop a similar chart of milestones in optical coating technology (harder, more stable and moisture resistant coating materials) and better production processes (more reliable, more precisely monitored, and allowing large area/high volume deposition).

The topic of antireflection coatings is vast, and it is impossible to review it comprehensively in an article of this size. Here an attempt is made to show how antireflection coatings evolved from inhomogeneous layers, through homogeneous layers with optical thicknesses that were multiples of a quarter wave of some central wavelength, to the modern non-quarter wave designs that, at times, may consist of many tens of layers. Antireflection coatings for the solution of a number of special problems are presented.

By comparing multilayer and rugate solutions to a typical rugate synthesis problem we demonstrate that rugate synthesis methods are still of a great importance. The new accurate algorithm for the synthesis of rugate coatings with arbitrary refractive index profiles is discussed. It is shown that this algorithm can be successfully applied for solving such classical rugate synthesis problem as reducing sidelobes accompanying stopbands of rugate filters.

Generally, the colour of the non-luminous objects in nature is due to absorption, diffusion and refraction of light. The colour of the optical coatings, as that of some kind of bird feathers, soap bubbles, butterfly wings, some insects, etc. is due to interference and therefore is named interference colour. This kind of colour belongs to the gonio-apparent or special-effect colours. Generally, industrial colorimetry does not deal with interference colour and the usual colorimetric instruments are inadequate to measure it. Only recently, with the new mica-pigment coatings, colorimetry is considering the measurement of the interference colour and new multiangle spectrophotometers are produced. This work is a general introduction to the ground of colorimetry and, at the end, deals with interference colours. A short overview is given of the Physiological Optics and of the Colorimetric Standards of the "Commission International de l'Eclairage" (CIE): particularly, Psychophysical Colorimetry, Psychometrical Colorimetry and Measurement Geometries are summarised. The colorimetry of gonio-apparent colours is considered. For a complete and detailed optical characterisation of interference colour the measurement of bidirectional transmittance and reflectance is needed. Particularly, basic elements for the colorimetric analysis of the interface between isotropic non-absorbing media and for thin monolayers are given.

A parallel was recently established between an empirical procedure for the estimation of reflecting thin film thickness and new results derived from a Fourier Transform (FT) thin film synthesis technique. For simplicity the proposed FT approach was limited to a particular case. The approach is generalized in the present work and practical considerations are discussed. It is shown that good results are possible although the generalized problem is more complex from the FT point of view.

In this communication, we discuss the behavior of the negative transparent-film transparent-substrate film-substrate system as a transmission-polarization-device. A transmission-polarization-device is defined as a device that produces pre-specified polarization changes of the electromagnetic wave upon transmission through the device. A comprehensive account of all devices is presented through the analysis of the transmission polarization function of the film-substrate system. We present device-specific closed-form design formulae for each and every device. We also present a general-device design-formula to design any and all transmission-polarization-devices. In this communication, thin-film coatings are treated as polarization devices.

The use of a photosensitive material for manufacturing the spacer of bandpass thin-film filters is a very attractive way for enabling the post-processing of such devices with the help of a light beam, either to correct with a high accuracy the consequences of some deposition errors on the filter properties (central wavelength out of specifications, inadequate spatial uniformity) or to create entirely new filtering devices with controlled spatial properties (for instance, variable filters with arbitrary profile). A theoretical presentation of the main problems arisen by such a laser trimming will be done, first for bandpass thin-film filters but also for multiple-cavity Solid Spaced Etalons (SSE). After a comprehensive analysis of the possible materials which can be selected for such an application, we will conclude our presentation by the description of the first experimental results obtained by our team in this new field, including a rapid presentation of the dedicated control means needed by this spatially localized approach of a filtering device.

Many optical methods are nowadays in use in the field of art. Most techniques are applied for characterization of materials, monitoring, diagnostics. Optical thin films can find an interesting application for artwork protection from the damage induced by illumination. The deteriorating effect of light on artworks is well known and the conventional approach to reduce the damage consists in lowering the radiation intensity and shortening the exposure duration. A complementary approach is to block all radiations that are not useful for viewing the artwork. A proper optical coating deposited on glass is able to cut the radiation flux at all wavelengths outside the range of sensitivity of the human eye. Glass is already in use in museum and galleries to protect artwork from vandalism and the use of coated glass can result in a simple method for contributing to art conservation. The optical coating will also improve the viewing because of the antireflection effect that can be combined with the protection properties. Particular care must be taken of this aspect because a compromise between conservation rules and visitor satisfaction must be reached. It is important that the thin-film coating does not introduce color alterations from the point of view of the observer and for this reason color testing on coated glasses must be carried out with real viewers.

Based on a special definition of the edge region of a thin-film interference filter, an approach to design steep-edge filters using the theory of equivalent layers is presented. Some features are discussed using the known theory to meet the topical filter requirements. An example is theoretically outlined and the spectral performance of a manufactured filter is presented.

Linear variables filters are band-pass multilayer coatings manufactured with a thickness gradient that allows a significant wavelength shift of the centring wavelength of the filter according to the point that is illuminated. In case such a filter is associated with a 2D matrix detector in order to form a compact spectrometer, iso-thickness lines must be as straight as possible, perpendicularly to the thickness gradient. To answer this problem, we developed a masking mechanism that combine the classical rotation movement of substrates and a translation movement for the mask, this last movement being induced during the rotation by the mean of a cam. Thickness gradient can be freely adjusted according to specifications, while transverse uniformity is 99.9%.

The concept of "Superprism" which is used in photonic crystal will be introduced into optical thin film coatings, due to the fact that the group velocity of the light is different as the wavelength in certain special case for the multiplayer thin film coatings. In this paper, The "superprism" effect of multilayer thin film coatings will be presented both from theoretical analysis and experimental results, these researches will create an new application of the thin film coatings not only to be a spectral filter but also can acts as "thin film gratings".

The production capabilities for optical multilayer coatings were improved significantly in the last decade. So called "shift free" coatings have become a standard in the coating production. Direct optical monitoring plays a key role to improve the layer thickness accuracy and takes advantage of error compensation effects. For the production of DWDM filters direct monitoring was introduced in the last decade. Continuous measurement is applied on relatively small substrate areas. (Ø < 200 mm). The paper reports substantial progress which has been achieved for coating systems with large area substrate holders (up to Ø 1050 mm). The stationary light spot of a single wavelength optical monitor is far out of centre of the rotating substrate holder. Intermittent monitoring on a substrate or a witness is applied. This technique enables rapid prototyping with tight specifications and high yields in large area batch coaters. Application results of challenging optical multilayer systems are demonstrating clearly the potential of this powerful monitoring technique. The monitoring capability was investigated for a lot of different layer systems such as dielectric mirrors, anti-reflection coatings, sophisticated edge filters, polarizer coatings, beam splitters and multiple cavity band-pass filters. Strong coincidence of theory with experiment was achieved with PIAD and magnetron sputtering. Reproducibility experiments have clearly shown the benefits of this monitoring technique.

We present a direct optical monitoring system that allows to minimize in-situ shift of parameters during process. In particular, we show how real-time optical monitoring on one or several lateral samples located on the same circumference of final components overcomes the problem of uniformity time dependence for long process and allows the fabrication of complex optical functions. Real-time signal processing on transmittance versus wavelength is used to determine in-situ refractive index of deposited material for each layer in the multilayer stack. It is shown how this method can be applied to the realization of quarter-wave and non quarter-wave stacks and the repeatability of a fully automated process is demonstrated for different components such as narrow band filters, polarizers or edge filters. Numerous experimental results from different deposition techniques are presented.

Inhomogeneous layers, such as so-called gradient index layers and rugate filters represent new and prospective thin film designs. Manufacturing such systems in practice requires calculation, deposition, monitoring and characterization of optical coatings with a well-defined continuous refractive index profile along an axis that is perpendicular to the film surface. Those coatings may be manufactured in the Leybold Syrus Pro 1100 deposition system by co-evaporation of SiO₂ and Nb₂O₅ as a sequence of several refractive index gradients. During these experiments our in-situ broadband monitoring system was used to measure the transmittance of the growing film directly at the rotating substrate. This additional information on the intermediate stages of the not yet completed film are extremely helpful in reverse engineering tasks, and clearly superior to the extent of information that may be drawn from the spectra of the completed film only. For characterization of these coatings a new model was developed, which significantly reduces the number of parameters. To generate a feasible parameter set, deposition rates for both materials recorded with quartz crystals monitor during deposition were used. This approach achieves a better accordance between in-situ measured transmittance and modelled transmittance than the intended design. During the optimisation process, a local minimization algorithm was used to vary the refractive index profile of the whole coating and film thickness of the intermediate stages. Finally, a significantly improved accuracy of the modelled transmittance was achieved.

The aim of this investigation was to study the characteristics of a reactive-low-voltage-high-current-ion-plating plasma and to correlate the observed plasma data with the properties of films deposited under such conditions. A Langmuir probe system (Smart Probe - Scientific Systems) was inserted into a Balzers BAP 800 ion plating plant above the e-gun evaporation source close to the insulated substrate holder. In this position during RLVIP deposition, plasma potential, floating potential, self-bias voltage, electron temperature, ion current density, and particle number density were measured and calculated, respectively. All measurements were performed in dependence of arc current (20-80A) and oxygen partial pressure (1 - 36 x 10^-4mbar). With rising arc current the number of charged particles, the self-bias voltage between plasma and substrates as well as the energy of the condensing and bombarding species were increased. These data explain the increase of density, refractive index and mechanical stress of RLVIP-metal-oxide-layers, like Ta₂O₅ and Nb₂O₅, deposited with higher arc currents. An increase of gas pressure decreased the energy of the particles and therefore reduced slightly film density and refractive index. However, it improved chemistry and eliminated unwanted residual optical absorption and also decreased compressive mechanical film stress.

During the last decade the ever increasing demand for both high-quality optical coatings and virtually deterministic deposition processes has led to a large number of ion sources available for deposition purposes. For a successful implementation of an ion source the prime economic objectives process stability and production yield have to be considered. The economic efficiency is strongly dependent on the temporal stability and spatial distribution of the ion current density and ion energy spectrum. Retarding Field Analyzers have demonstrated their potential as a tool for the analysis of ion sources. However, deliberate evaluation of the measurements is required especially at a non-zero angle of incidence occurring during the examination of three dimensional ion emission profiles. The present study discusses the influence of different geometric Faraday-Cup designs on the resulting data as well as erroneous conclusions potentially drawn from measurements. Furthermore first results of the ion current density distribution characteristics of different ion sources, evaluated on the basis of data taken by a multicup array are presented.

Fluoride materials like Magnesium fluoride and Lanthanum fluoride exhibit unique properties for applications in mirror and anti reflecting coatings in the VUV spectral range (120- 230 nm). These large band gap materials provide low absorption and a usable refractive index contrast. Common deposition methods are thermal evaporation and electron beam evaporation. A columnar microcrystalline structure with a significant porosity is observed for such coatings. Furthermore, a high sensitivity for contamination processes resulting in an increasing absorption is often perceived. Investigations of mirror systems exposed to a harsh environment like the storage ring free electron laser at ELETTRA show a rapid degradation in respect to a reduced reflectivity, an increased hydrocarbon contamination, and a formation of colour centres. An improved performance of the fluoride coatings could possibly be expected for films, which do not have the polycrystalline columnar structure. Ion beam sputtering deposition of fluoride materials demonstrated its applicability to deposit dense amorphous fluoride coatings down to 193 nm. An IBS deposition plant with a Kaufman ion source, using a reactive fluorine environment, is used to grow fluoride layers with comparably low absorption values. Single and multilayer coatings were optically characterised after deposition, exposed to synchrotron radiation at ELETTRA, and characterized again after irradiation. However, the first set of irradiated multilayer mirrors showed a strong degradation of reflectivity and a strong hydrocarbon contamination. Colour centres were not observed.

Schott's already commercially available two layer Ta/SiO2 phase shift system can be tuned from 6% up to 40% transmission for 157, 193 and 248 nm lithography wavelengths. Thus one film patterning process provides a wide product range. Attenuated phase shift masks for 6%, 20% and 30% transmission at 193nm were produced. Tests for laser stability and chemical durability show excellent performance. The phase shifting film achieves a high etch selectivity to the substrate. Dry etch process development is done at IMS chips in Stuttgart, Germany, to provide our customers the service of a good start process for patterning. Results of phase and transmission uniformity are included. Our newest development enhances the layer system and provides a better contrast for inspection in reflection mode. Transmission of our standard two layer Ta/SiO2 PSM system is below the required 20% at inspection wavelengths. The reflectivity of 30% to 40% can be lowered by insertion of an additional contrast layer. The thickness of this contrast layer is adjusted to achieve the required reflection at inspection wavelengths, while the other film thicknesses are tuned to preserve the desired transmission and 180° phase shift at the design wavelength. As first examples 6% and 20% transmission PSM for 193 nm were tested. Reflection at 257 nm and 365 nm inspection wavelengths can be lowered from initial 30% to 40% down to about 10%.

Amorphous layers of metal oxides deposited by Plasma Ion Assisted Deposition (PIAD) are widely used in the field of optical coatings due to their salient properties which enable the deposition of complex multilayer stacks. However, their use in the Deep UV spectral range is restricted as the range of transparency is limited by the absorption due to the first electronic band transition. The only oxide suitable for applications at 193 nm seems to be Al₂O₃ for which a band gap energy of 8.7 eV (143 nm) is reported for the crystalline state. Yet for thin layers of Al₂O₃ no work reports the making of absorption free layers at 193 nm. In this study we investigate how the amorphous structure of PIAD-deposited Al₂O₃ thin films influences the electronic structure and as a consequence of that the absorption behaviour for wavelengths close to the absorption edge. The electronic structure is worked out by a theoretical approach where in a first step the geometric structure is simulated using a Monte Carlo approach. Using this geometric structure the electronic structure is calculated by the tight-binding method in a second step. With these data absorption spectra are calculated and compared to measurements on PIAD Al₂O₃ layers. The experimental data for the start of the absorption lie on the longer wavelength side of the limit set by the amorphous structure - a fact, that encourages further work on the optimization of the deposition parameters.

The requirements to produce high performance coatings increase dramatically when moving from 248 nm to 193 nm. The quality of DUV thin film components is mainly determined by the optical properties of the applied layer materials. The reduction of losses due to scattering and absorption of dielectric materials is essential for excellent properties of the coating results. The most common oxide and fluoride materials SiO₂, Al₂O₃, MgF₂ and LaF₃ have been investigated and optimized. Plasma ion assisted deposition was applied for the deposition of the oxide materials, using improved coating equipment such as the modified APSpro (advanced plasma source). The paper reports the results of DUV coatings using plasma ion assisted deposition for the oxide materials. Single layers of silica and alumina and multilayer systems with both materials were investigated. In addition, MgF₂ and LaF₃, conventionally coated at very high temperatures, have been performed to demonstrate the improved capabilities of the optimized SYRUSpro DUV for DUV applications with all the new features.

This paper deals with the approaches to preserve the high reflectance aluminum mirror for the VUV spectral region. Single fluoride and oxides layer, homogeneous multilayer and hybrid multilayer solutions are put forward. Single fluoride and oxides materials have achieved reflectance above 90% at 193 nm.

The present candidates for low loss dielectric optical coatings at VUV excimer laser wavelengths are fluorides. Within this group, only one material - namely lanthanum fluoride - is used almost exclusively as high index film material. In search of additional high index film materials for use in VUV we investigated a broader spectrum of lanthanide tri-fluorides since little is known about their properties and the advantages or disadvantages with regards of their use in DUV- and VUV - optical stacks. Fluorides of lanthanum, neodymium, samarium, gadolinium, ytterbium and also yttrium were evaporated thermally. Precision VUV-measurement were initiated to give an overview of the ranges of UV-transparency up to the absorption edges and to determine the optical indices of these coating materials. Supplementary, also stress measurements, atomic force microscopy and XRD measurements were performed to scrutinize the properties of the films.

Since excimer laser applications extend to deep and vacuum UV wavelengths at 248 nm, 193 nm and 157 nm, renewed research interest has recently arisen on fluoride thin films due to their unrivaled position as wide-band-gap material for the vacuum UV (VUV). Among these materials, only a very limited number can act as the high refractive index component in multiplayer interference stacks. Besides LaF₃, gadolinium tri-fluoride is a potential candidate especially for wavelengths at about and below 200nm. We report on the evaluation of the structural properties, the optical properties with emphasis to the DUV - spectral range, and the mechanical properties of GdF₃ single layer by means of XRD, GIXR, AFM measurements, spectral photometry and by ex - situ mechanical stress analysis using the laser beam deflection method to measure the substrate deformation. The samples were deposited onto fused silica and silicon substrates by a low-loss evaporation technology in a BAK 640 coating plant applying various deposition conditions.

The performance of optical coatings for high power DUV/VUV laser applications depends amongst others on residual absorption in the thin film layers due to impurities or defects. Using pulsed F₂ laser induced fluorescence measurements (LIF), characteristic non-intrinsic emissions of praseodymium, cerium and hydrocarbons are identified for several high reflecting AlF₃/LaF₃ based mirrors on CaF₂ substrates. The separate investigations of single AlF₃ and LaF₃ layers on silicon wafers indicate that these emissions result from the LaF₃ material. The amount of the impurities, however, varies strongly between different LaF₃ material grades. The influence of different LaF₃ material grades on the absorption properties of high reflecting mirrors is measured for the first time upon ArF laser irradiation using the laser induced deflection technique (LID). Low absorption values of less than 1*10^-3 are obtained for all samples. The absorption, however, varies by more than a factor of 2 which is correlated to the appearance of the praseodymium and cerium emissions in the LIF spectra.

The persistent utilization of optical lithography at the DUV and VUV excimer laser wavelengths leads to extraordinary demands on the optical components involved (high throughput, low scattering, high mechanical stability, ...). Fluorides are the main or even the only candidates for film materials in these spectral regions because of their low absorption. There are several high-index and low-index fluoride materials. These materials, however, may significantly differ in their nanostructural properties leading to scatter losses crucially influencing the performance of the multilayers. In order to find optimal material combinations, HR multilayer mirrors were fabricated using several high-index fluoride film materials. Spectral photometry, atomic force microscopy, as well as total and angle resolved light scattering measurement and analysis were performed for comprehensive characterization.

To develop beam splitters for soft X-ray laser Mach-Zehder and Michelson interferometer at 13.9 nm, Mo/Si multilayers deposited on back side and both sides of silicon nitride with thickness of 100 nm were fabricated using DC magnetron sputtering. We presented the results of their reflectivity, transmission and probing the electron density of laser-produced plasma using a soft X-ray laser Mach-Zehder interferometer. The design and fabrication of broadband polarizers were also presented in this paper. These polarizers can be used as analyzers for a wideband polarization measurement. We discuss the results obtained with depth-graded Mo/Si multilayer analyzers for 13-19nm polarization measurements. We also discussed the development of X-ray supermirrors used as broadband angular reflectors operating at the fixed energy of 8 keV. We summarized our recent investigation of the design, fabrication and performance of depth-graded W/Si, W/C and W/B₄C multilayers.

Most applications of Mo/Si multilayer optics in EUVL require a high normal incidence reflectivity. Using dc magnetron sputtering we achieved R = 68.8 % @ λ = 13.5 nm. Different interface-engineered Mo/X/Si/X multilayers with maximum reflectivity of 69.6 % at 13.5 nm were developed. These new multilayer mirrors consist of molybdenum and sili-con layers separated by different interdiffusion barriers (X = C and SiC). Microstructure and optical properties of the multilayers have been investigated by small and large angle Cu-Kα scattering, AFM and characterized by EUV reflectometry. A concept for material selection, thickness optimization of interdiffusion barriers and perspectives for their wide application in imaging EUVL optics will be discussed. Some applications of multilayer mirrors in EUVL require not only the highest possible normal incidence reflectivity but also a long-term and thermal stability at the operating temperatures. The Mo/C/Si/C interface-engineered were optimized in terms of high peak reflectivity at a wavelength near 13.5 nm (R_p ⩾ 60.0 %) and broad operating temperature range (T = 20 - 500°C). The best results were obtained with 0.8 nm thickness of carbon interlayers on both interfaces. Annealing in vacuum was carried out at elevated temperatures up to 650 °C for up to 100 hours. The combination of good optical properties and high thermal stability of interface - engineered Mo/C/Si/C multilayer mirrors underlines their potential for their use in EUVL optics.

In the race towards attosecond (as) pulses for which high order harmonics generated in rare gases are the best candidates, both the Harmonic spectral range and spectral phase have to be controlled. We present in this proceeding four mirrors numerically optimized and designed to compensate for the intrinsic Harmonic chirp recently discovered and which is responsible for a temporal broadening of the pulses. They are capable of compressing the duration down to 100 as. We present the fabrication of those aperiodic multilayers and show the measurement of reflectivity, which prooves that those multilayers are in agreement with the specifications and so let us think that they will be able to compress attosecond high harmonics trains.

We present an experimental study of aging and thermal stability of Sc/Si multilayers deposited by magnetron sputtering. These multilayers have been characterized by using hard X-ray grazing incidence reflectometry at 0.154 nm and synchrotron radiation reflectometry at near normal incidence. The reflectivity was found to be stable after one year. A maximum reflectivity of 46% has been measured at 46 nm. However a 20% relative decrease of the reflectivity have been observed after one hour thermal annealing at 200°C. In order to improve thermal stability, we studied two different barriers layers (B4C and ScN ). We compare the decrease of peak reflectivity and its wavelength shift after one hour annealing at 200°C under argon atmosphere. The best result was observed with the design using 0.3 nm B4C barrier layers. A relative decrease of 2% of the reflectivity peak has been observed with this design as compared to a 20% decrease without barrier layers.

Laser resistant coatings are needed for beam steering (mirrors), pulse switching (polarizers), and high transport efficiency on environmental barriers (windows / lenses) on large laser systems. A range of defects limit the exposure fluence of these coatings. By understanding the origin and damage mechanisms for these defects, the deposition process can be optimized to realize coatings with greater laser resistance. Electric field modeling can provide insight into which defects are most problematic. Laser damage growth studies are useful for determining a functional laser damage criteria. Mitigation techniques such as micro-machining with a single-crystal diamond cutting tool or short pulse laser ablation using the burst technique can be used to arrest growth in damage sites to extend optic lifetime.

The laser damage resistance of optical coatings is a critical point for a large number of applications. However improving this resistance is often hard to obtain because of the large number of parameters in the deposition processes than can modify the laser damage threshold and the lack of detailed and exploitable studies published on this subject. Then, the aim of this work is to test and analyze the laser damage resistance of a usual material for high power applications (silica) deposited in various conditions. The thin films of different thicknesses were specially deposited using different techniques available at the Institut Fresnel: Dual Ion Beam Sputtering, Electron Beam Deposition, Ion Assisted Deposition and Ion Plating. The laser-induced damage thresholds of these coatings were determined at 1064nm and 355nm using nanosecond pulsed YAG lasers, with a 1-on-1 test procedure. Other diagnostic tools were used to complete the study and make potential correlations with laser damage: photothermal techniques, luminescence spectrocopy, optical profilometry, dark field and Nomarski microscopy. The comparative study of these results highlight different laser damage behaviors of the silica coatings that we correlate to the density and the nature of the defects.

We present Laser Induced Damage Threshold (LIDT) results on multilayer components with different optical functions for near infrared applications. In this paper, we investigate the different fabrication steps of such functions. In particular, we show experimental results on surface preparation (polishing, cleaning,) and on deposition techniques (Ion beam assisted process) related to the materials involved in coatings. Laser damage tests are performed at 1064-nm with a 5-ns pulse Nd:Yag laser and experiments are made at surfaces of optical components using a 12 μm diameter focused beam. Accurate damage probability curves are plotted thanks to a reliable statistical measurement of laser damage. Use of a statistical model permits to deduce the densities of laser damage precursors. A systematic analysis of all the steps involved in fabrication allows then to build multilayer components with high laser induced damage resistance.

New developments of laser thin films for high power laser systems were reviewed. Special attention was paid to several key coatings which bottlenecked the higher power laser system, such as pick-off mirrors, large aperture polarizer and YAG harmonic wavelength splitter, as well as AR coatings. Defects were deemed to be the initial and essential source of laser-induced damage. The investigation of the original control of defects was focused on the deposition process control, such as substrate cleaning, purity of deposition materials, deposition temperature, oxygen pressure in vacuum chamber and so on. Several methods of evaluation of laser damage were employed, which included Laser Induced Damage Threshold (LIDT) determination and absorption detection based on Surface Thermal Lensing (STL) technique, as well as Total Integrated Scattering (TIS) measurement. The LIDT of pick-off mirrors reached to 20 J/cm² (1064 nm, 1 ns), meanwhile the LIDT of the ultraviolet coatings did to 8 J/cm² (355 nm, 1 ns) because of its comprehensive mechanism. The LIDT of third harmonic mirror could be improved effectively with post-treatment methods, such as oxygen-plasma post-treatment and vacuum annealing. Actually the situation of the laser thin films with very high damage threshold was complicated due to their uniformity of optical properties and stress induced surface deformation in the large aperture.

The initial motivation for the development of Ion Beam Sputtering (IBS) processes was the need for optical coatings with extremely low optical scatter losses for laser gyros. Especially, backscattering of the gyro-mirrors couples the directional modes in the ring resonator leading to the lock in effect which limits the sensitivity of the gyro. Accordingly, the first patent on IBS was approved for an aircraft company (Litton) in 1978. In the course of the rapid development of the IBS-concept during the last two decades, an extremely high optical quality could be achieved for laser coatings in the VIS- and NIR-spectral region. For example, high reflecting coatings with total optical losses below 1 ppm were demonstrated for specific precision measurement applications with the Nd:YAG-laser operating at 1.064 μm. Even though the high quality level of IBS-coatings had been confirmed in many applications, the process has not found its way into the production environment of most optical companies. Major restrictions are the relatively low rate of the deposition process and the poor lateral homogeneity of the coatings, which are related to the output characteristics of the currently available ion sources. In the present contribution, the basic principles of IBS will be discussed in the context of the demands of modern laser technology. Besides selected examples for special applications of IBS, aspects will be presented for approaches towards rapid manufacturing of coatings and the production of rugate filters on the basis of IBS-techniques.

This paper addresses different highly reflective optical coatings on micro scanning mirrors (MSM) for applications in the NIR-VIS-UV-spectral region to enable new applications at high optical power density like laser marking and material treatment. In the common case of MSM with an unprotected Al coating, the absorption limits the maximal power density because of induced heating. In contrast to macroscopic optics HR-micro mirror coatings have to guarantee additional demands like low-stress and CMOS compatibility. Hence, to enable novel high power applications of MSM in the NIR-VIS-UV spectral region highly reflective low-stress coatings have been developed according to a triple strategy: (a) broadband metallic reflectors, (b) dielectric multilayers and (c) enhanced hybrid coatings. For Au and Ag based NIR-coatings an excellent mirror planarity and a reflectance around 99 % (@ 1064 nm) have been achieved, whereas dielectric coatings reached 99.7 % for a (LH)⁴ design and thinner low-stress hybrid NIR-coatings reached up to 99.8% enabling an improved mirror planarity and excellent laser damage threshold. For the VIS and UV spectral region enhanced hybrid HR-coatings have been favored, because they enable high reflectance of up to 99.7 % @ 633 nm or 98.8 % @ 308 nm in combination with low stress, high mirror planarity and CMOS compatibility.

The optical properties of TaZrO_x mixed oxide thin films are investigated. The films were deposited by reactive pulsed magnetron sputtering in a double magnetron set up using two Ta and Zr metallic targets. Depending on the mixture of the materials, crystallization at different temperature occurs. For a specific mixture, temperature stability of more than 950°C could be demonstrated. This is more than another value of TiAlO_x thin films reported very recently.

Ag-dielectric multilayers are widely used in the production of heat reflecting filters, induced transmission filters, beam splitters, etc. The performance of such coatings in the visible part of the spectrum is sometimes strongly influenced by a plasmon absorption in the Ag-layer or a surface plasmon absorption in the Ag-dielectric interfaces. The strength of the plasmon absorption is very sensitive to the layer structure, the light polarization and the angle of incidence. As a result, the target specifications for reflection and transmission are not reached easily. We investigate PVD-deposited TiO2-Ag-TiO2 multilayers by means of optical reflection and transmission and Grazing Incidence X-ray Reflectometry (GIXR). The GIXR-method yields the individual layers thicknesses and the interface roughness. Some of the coatings have a broad absorption peak between 500 and 400nm that cannot be modeled using the bulk dielectric function of Ag. The magnitude of the absorption peak is correlated with the measured roughness of the TiO2-Ag interfaces. The analysis of the results shows the critical parameters for the deposition process.

"Closed field" magnetron (CFM) sputtering offers a flexible and high throughput deposition process for optical coatings and thin films required in a wide range of optical applications. 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. Fine layer thickness control and deposition of graded index layers is also assisted with a specially designed rotating shutter mechanism. The CFM configuration also allows plasma treatment of surfaces prior to deposition, allowing optimisation of coating adhesion to substrates such as plastics. This paper presents data on optical, durability and environmental properties for CFM deposited optical coatings, including anti-reflection, IR blocker and colour control and thermal control filters, graded coatings, as well as conductive transparent oxides such as indium tin oxide. Benefits of the CFM sputter process for a range of optical applications are described.

Future production of high quality laser components asks for both, the precise preparation of low loss multilayer stacks and a clean room compatible innovative deposition process. In addition a cost-effective thin film filter production is required in order to transfer new developments like ultra fast pulse laser technique from research to economical products and applications. One of the most promising candidates is magnetron sputtering due to the potential of excellent film properties, a fully automatic clean room compatible manufacturing process and a high productivity. Similar film qualities as with ion beam sputtering are realised but with a more than 10 times higher productivity. The reproducible production of multilayer broad band mirrors with controlled group delay dispersion and low losses is still a big challenge. Promising results were achieved on the basis of silica and niobia and will be presented.

This paper discusses improvements in manufacturing of coated infrared optical components. Such components often have key functions in defence, security or space applications and must withstand severe environmental conditions. Therefore, very durable coatings are desired. As a consequence of its radioactivity the formerly used low refractive index material thorium fluoride is substituted. Examples for beam splitter cubes contacted with novel infrared transparent cement, interference filters, mirrors and AR coatings are presented.

Optical coatings have been deposited by pulse magnetron sputtering of the target materials silicon and aluminium using the reactive gases oxygen, nitrogen and fluorine. The measured refractive index and roughness of the SiO₂, Si₃N₄, Ta₂O₅ and Al₂O₃ films indicate the deposition of very dense and smooth films. Absorption of SiO₂ and Al₂O₃ films is low even at a wavelength of 193nm. The sputter deposited AlF₃ layers have low absorption until 150 nm but then show an absorption edge. Examples of multilayer include antireflective coatings for ophthalmic lenses and cut filters consisting of up to 150 λ/4 layers. These films were produced at a single stationary coating station without interruption of film deposition by changing the reactive gas during the plasma process. This process was also used for the deposition of rugate filters with apodisation function by continuous variation of the reactive gas composition during the deposition.

Improvements of the environmental stability of inorganic optical coatings on polymer substrates are expected from a slight variation of the chemical composition of SiO₂ films by organic modification through the addition of gaseous hexamethyldisiloxane (HMDSO) to a classical plasma ion-assisted deposition process. The influence of several process parameters on the chemical composition of these coatings has been studied on polycarbonate, quartz glass and silicon substrates to define an optimum range of process parameters with regard to the useful properties obtained of the coated polymer optical component.

Inhomogeneous coatings are promising for superior optical properties, e.g. broadband antireflection, in comparison to conventional HL-stack designs. Although a lot of excellent theoretical work on optical behaviour of rugates and gradient index films has been done during the last decades, there is no real breakthrough in industrial fabrication. The realization of such coatings leads to an extensive and time-consuming computer-aided control, because of complicated layer designs with continuously changing refractive index gradients. We describe the design and optical performance of an omnidirectional antireflection coating that essentially represents a hybrid coating composed from homogeneous layers and linear refractive index gradient layers.

Transparent conducting coatings and patterns of ITO (indium tin oxide) were deposited by a direct gravure printing on PET foils using nanoparticle-based UV-curable inks. Solid areas with thicknesses ranging between 300 and >1000 nm were obtained by varying the ink composition (e.g. ITO content, solvents) and fundamental parameters of the printing plate such as the line density. The best ITO coating patterns showed a sheet resistance of 3 to 10 kΩ_□ and a transmission of up to 88 % with a haze of less than 1 %. One of the most crucial steps during film formation is the drying of the wet film as it changes the rheology and polarity of the ink and in consequence decisively influences the film formation. Typical fields of application of the gravure-printed ITO patterned electrodes include smart windows, flexible displays and printed electronics.

Thin Nb₂O₅-films were deposited on unheated glass, fused silica, and silicon substrates by reactive-low-voltage-high-current-ion-plating (RLVIP). Optical as well as mechanical film properties and their environmental stability are remarkably influenced by deposition parameters like e. g. arc current, deposition rate, gas composition, and total gas pressure. It was found out that an arc current around 50A, gas mixtures with high amount of oxygen, and a deposition rate around 0,3nm/s yielded the best results. Refractive indices were calculated from data obtained by spectrophotometric intensity measurements of the constrained amorphous and homogeneous films. Residual optical absorption in the film's high transmittance range was determined by photothermal deflection spectrometry. Mechanical film stress, for dense films always compressive, was measured by deformation of coated thin silicon discs. Typical obtained values are n₅₅₀ = 2,39 - 2,40, k₅₁₅ = 2×10^-4, σ = -30MPa. Detailed information is presented in diagrams.

In this paper we describe how optical coatings can be deposited uniformly with a high precision and reproducibility on 3-dimensional substrates, such as spherical lenses, by CVD. We present results that will highlight some specific advantages of CVD over the traditionally used methods of e-beam evaporation and magnetron sputtering and we will show that CVD has tremendous potential for enhancing the quality of optical coatings and for making cost savings.

The ion assisted thin film deposition (IAD) method has been used extensively for more than two decades, but questions about possibility of improving of the laser-induced damage threshold (LIDT) by this method compared with the conventional electron-beam evaporation (non-IAD) method are still not fully answered. A more complete understanding of different factors that can influence laser-induced damage threshold is necessary for continued development of multilayer dielectric coatings optimized for high-power laser applications. To clarify these factors we performed comparison of LIDT for IAD and non-IAD coatings in nanosecond and femtosecond pulse ranges. High reflectance mirrors at 800 nm and 532 nm were tested. Mirror coatings were made of ZrO₂ and SiO₂. Automated LIDT measurements were performed according to the requirements of current ISO 11254-2 standard. Two lasers were used for the measurements: Nd:YAG (λ = 532 nm, τ = 5 ns) and Ti:Sapphire (λ = 800 nm, τ = 130 fs). Measurements at 800 nm and 532 nm were performed at 1-kHz and 10 Hz pulse repetition rate respectively (S-on-1 test). The damage morphology of coatings was characterized by Nomarski microscopy and relation of LIDT with coating parameters was analyzed.

An investigation of laser-induced damage thresholds (LIDT) of antireflection coated lithium triborates used for second and third harmonic generation were performed at 1064, 532, and 355 nm wavelengths for ~4 ns pulses. Two types of coatings were tested: an anti-reflection coatings with dual peak at 1064 nm and 532 nm and anti-reflection coatings with three peaks at 1064 nm, 532 nm, and 355 nm, respectively. Ion-beam sputtering and magnetron sputtering technologies where used for coatings deposition. Automated LIDT measurements were performed according to the requirements of current ISO 11254-2 standard. The obtained LIDT were in range of 3-15 J/cm².

Materials involved in gas sensing applications have been deposited by various methods in thin film form. Variation of the optical properties of the thin films were investigated under butane and ozone exposure using the m-lines technique. Effective index variations down to 10^-4 were observed. Concentrations of 100 ppm of butane diluted in the air or in nitrogen were detected.

In the field of microelectronics, the Extreme Ultraviolet (EUV) lithography operating at λ=13,5 nm, appears, today, as the most promising future technology. The viability of this next generation technology has, however, to face several technical issues. Among them, the realisation of highly reflective EUV mirrors is one of the key issues and concerns the mirrors for light transport as well as the lithography masks. In this last case, the mirrors which consist in a periodic Mo/Si multi-layer coating deposited by ion beam sputtering suffer from reflectance limitations and thermal instabilities. In this paper, an experimental investigation on IBS deposited Mo/Si multi-layers is presented. The study is mainly focused on the formation of Mo/Si interfacial zones and their evolution with thermal annealing up to 600°C. Detailed investigations by high-resolution transmission electron microscopy (HRTEM) and energy filtering TEM have been performed in association with differential scanning calorimetric (DSC) analyses. For the purpose, dedicated samples were prepared enabling the identification of phase transformations occurring during thermal annealing. It will be shown, in particular, how this coupled characterisation approach (TEM+DSC) can help understanding the interface growth in such metal/silicon systems. The characterisation results are presented and discussed.

Thin films of Zr-silicate were deposited on silicon and BK7 glass substrates by EB co-evaporation. The mixing thermodynamics of the ZrO₂ - SiO₂ system was analysed. Chemical bonding in Zr-silicates has been studied by X-ray photoelectron spectroscopy. The structural and optical properties and the surface morphology were investigated.

Nowadays, chirped dielectric mirrors for ultrafast optics and laser applications are usually manufactured by sputtering techniques. The suitability of Advanced Plasma Source (APS) assisted electron beam evaporation with respect to such coatings is still under investigation. The purpose of this presentation is to show our first results of the deposition of chirped layers produced by plasma ion assisted electron beam evaporation and of the investigation of their properties. The aim was to design and prepare a NIR-mirror for the spectral range of 700 nm to 900 nm. It has been attempted to find a design that is robust with respect to errors of thickness and refractive index. The mirror consists of more than 26 layers composed of alternating high- (Nb₂O₅) and low-refractive index (SiO₂) material. The deposited coatings were tested in terms of their group delay dispersion (GDD) and their reflectivity. We show, that in the wavelength range between 720 nm and 890 nm the GDD exhibits a value of about -50 fs², whereas the reflectivity is above 99%. However, the subsequent reverse engineering operations show a relatively large thickness error of more than 1% - 2% regarding the particular layers. Nevertheless the effect on the GDD and the reflectivity is tolerable. Furthermore, we present our first experiments concerning the design and fabrication of a chirped mirror, which allows controlling the third order dispersion (TOD), whereas the relative thickness error of the particular layers should not exceed 1%.

Rugate structures, as well as gradient refractive index films in general, attract a lot of interest. The gradient index systems may provide advantages in both, optical performance and mechanical properties of the optical coatings. Rugates have shown to be especially interesting for design of notch filters. A lot of theoretical work on design of rugate filters has been done in the last decades. However, only few of the designs could be deposited, which is often caused by practical problems, e.g. preparing materials with the desired refractive index values. In this paper two different gradient refractive index designs are compared to a classical high-low stack. One gradient design is synthesized by an apodized sinusoidal structure that is approximated by homogeneous sublayers. The other one is based on an apodized sinusoidal structure as well, but it is approximated by a hybrid structure, i.e. a combination of linear gradient index ramps between the lowest and the highest refractive index applicable and homogeneous layers of high index values. The two gradient designs take into account the constraints posed by limitations of the real deposition systems. Both designs are compared to a classical high-low stack and the advantages and drawbacks of each approach are commented.

Properties of 3 types of multilayer dielectric chirped mirrors manufactured with Helios Leybold system (magnetron sputtering with plasma/ion assisted technology) are discussed. The first type includes mirrors providing negative group delay dispersion (GDD) and high reflectance in a wavelength range 650-1150 nm. Such mirrors are used in a broadband Ti:Sapphire oscillator for generating sub-6 femtosecond pulses. The second type of mirrors has extremely low both GDD oscillations and losses in a range 740-840 nm. Such mirrors are of interest for both long-cavity high-energy Ti:Sapphire oscillators and so-called external cavities for storing energy from femtosecond oscillators. The lowest residual GDD fluctuations achieved for this type of mirrors are 5 fs². The third type is high reflectors with very high reflectivity. Different coating materials: Nb₂O₅, TiO₂, Ta₂O₅ together with SiO₂ are compared for these 2 types of mirrors. The results of reproducibility of such mirrors and their characterization in terms of reflectivity, losses, surface quality are presented. Comparison of the design with the manufactured mirror is also done.