The Berlin scientist and educator Wilhelm Zenker first proposed the principle of color selection by recording standing waves in photographic media. This principle is often applied in modern optics.

PICVD is used for providing organic spectacles with a protective hardcoat, an antireflective multilayer and a hydrophobic top coat. The hardcoat, low index material in the antireflective stack and the hydrophobic film are derived from the same silicon precursor, different layer properties can be achieved by tuning of the plasma parameters. For the high index material, TiO₂ is used. The coating performances of Carl Zeiss Carat Carat-coating can readily be achieved. In contrast to standard batch coaters, allowing to coat up to 100 spectacles at a time, the PICVD technique uses a single station design: the spectacles are coated in a single reactor each at a time. This single station concept result in cost effective coating processes and allows furthermore to reduce the turn-around time of the coating service dramatically: almost one day can be saved compared to the mainstream procedure, comprising of hardcoating with lacquer, post bake, washing and batch coating of AR stack, respectively. Optical and mechanical properties of the low index films depend strongly on the oxygen content of the precursor. Measurements of the films' refractive index and hardness are presented and conclusions for optimizing the hardcoat and the low index film are drawn.

Diamond like carbon (DLC) can be an ideal candidate as coating material for optical components owing to its high hardness value, chemical inertness and high transparency in the IR spectral region. DLC thin films have been deposited by RF magnetron sputtering from a graphite target in argon atmosphere without hydrogen on glass and silicon substrates in order to study the influence of some parameters on the mechanical and optical properties. Increasing the power input values, from 100W to 400W, the DLC films compactness increases too as it can be deduced from the raise in this range of power of both hardness and refractive index values, calculated by microindentations size and reflectance and transmittance spectrophotometer measurements respectively. Moreover, a set of sample was deposited at different substrate temperatures and at the highest used value a lower value of hardness and refractive index as well are obtained. The possibility to correlate the films compactness to their absorption humidity has been investigated by means of the IR transmittance spectra analysis. Densifying effect of RF sputtered DLC thin films examined in this work seems to be related, in conclusion, to the power input increasing rather than to the substrate temperature.

In this work, ZnSe thin films were deposited by radio frequency magnetron sputtering onto oriented silicon substrates. Three sets of samples were produced by varying the argon working gas pressure, and changing the sputtering power supply. The effect of the different growth conditions on the structural and optical properties of the ZnSe films was investigated by using XRD and FTIR spectroscopy. In particular, x-ray diffraction was used in order to study the residual strains and texture. The ZnSe coatings were grown in the cubic polymorph with the grains preferentially oriented for all the investigated pressures with the exception of 0.5 Pa. An in-plane residual stress reversal, which changed from compressive to tensile by going from the low to the high-pressure sample set, was observed. At the 0.5 Pa pressure, the ZnSe coatings were both in compressive and tensile state, according to the power supply value. These result have been correlated with the momentum of reflected neutral in order to find an exhaustive description of the deposition process. At low momentum values, the ZnSe films show tensile state, low refractive index, grains preferentially oriented, while at high momentum they were in compressive state, refractive index very alike to the bulk and grains randomly oriented.

Plasma-IAD with the APS has been applied for a large number of different layer systems in production an ind R and D. The ability for the production of shift free multilayer coatings for the visible and NIR spectral range is utilized in manufacture for many applications such as steep edge filters for color separation, rugate filters for laser protection and narrow-bandpass filters for wavelength division multiplexing. An overview was given. Shift free narrowband filters for the UV-B region were published in 1996. The paper reports the result of UV coatings using plasma ion assisted deposition. Tantala/silica and hafnia/silica combinations have been used for multilayer coatings in the UV-A and UV-B spectral range. Single layers of silica and alumina and multilayer systems with both materials were investigated in the UV-B and UV-C region. The coatings were characterized by obtained transmittance and reflectance curves as well as absorption and scattering measurements. The temperature stability results are compared with coatings in the visible and NIR spectral range published.

The diamond like carbon (DLC) is very hard, inert to chemical attack and transparent in the IR region. In order to increase the transparency of DLC, the percentage of Sp³ bonds must be increased. In this work, thin film of DLC were deposited by the Dual Ion Beam Sputtering technique. An argon ion beam sputters a graphite target and a second one assists the film during the growth. A set of samples were produced at different momentum transfer varying the energy and current density of assisting ion beam and the growth rate. The momentum transfer is defined P equals n_c divided by n_at (root) 2 m_c E_c where n_c is the number of recoiling carbon atoms, m_at is the number of the carbon atoms in the volume interested at the collision cascade process and E_c is the energy of the recoils after the collision with the Ar ions, n_c, n_at, and E_c were calculated by the TRIM program. THe optical properties as the optical gap of the samples were related to the momentum transfer value. As far as the mechanical properties were concerned, the hardness value was measured by Knoop microindentation for all samples.

One of the main responsibilities for adhesion failure of antireflection coatings on plastic substrates is the stress developing at the film/substrate interface during film deposition and subsequent system cooling. Coating a substrate by a different material always induces stress at the interface, because it enforces the film to copy the substrate structure. Further, non-equilibrium conditions during film growth and thermal deformations due to post- deposition cooling, also contributes to the total stress of the system. In particular, thermal stress plays an important role in adhesion failure of coated plastic,s because the expansion coefficient of polymers is about an order of magnitude greater than that of hard oxides. In order to prevent delamination of the film, this strain must be balanced by bond strength between the film and the substrate. In this work, we investigate the possibility of improving the film/substrate adhesion by reducing the total stress at that interface. In fact, the intrinsic stress of ion assisted hafnium oxide films is influenced by the assistance conditions, and consequently the total stress can be changed by varying the experimental parameters. Hafnium oxide layers were deposited on plastic substrate by dual ion beam sputtering, at different growth conditions. Stress values were obtained by measuring the curvature of the substrate before an dafter deposition. Practical adhesion properties were evaluated by mechanical tests.

SiO₂, Ta₂O₅ and MgF₂ have been deposited by electron beam evaporation under bombardment of ions generated by three different ion or plasma sources. Multilayer systems containing 5 to 12 layers have been designed and realized. The maximum reflectance R of a glass/air interface can be reduced down to R < 0.5 percent in a spectral region of 400 nm to 700 nm with each of such AR coatings mostly exceeds that of all-oxide system in the shorter wavelength region. With scanning scratch test the scratch resistance of the coatings have been determined relative to each other.

REOSC has developed a new hard multispectral coating on ZnS compatible with military environment conditions. In extreme conditions the coating exhibit a pretty good behavior. Developed on ZnS, other substrates can be used. The coating itself can be tuned from UV up to 10micrometers . High transmission in visible spectrum >= 90 percent is achievable for an antireflection coating tuned around 8-10 micrometers on ZnS. The coating is laser compatible.

A Mark II gridless ion source and HCES5000 hollow cathode electron source are used for ion assisted deposition (IAD) of dense coatings. It is possible to check the ion beam profile with a beam probe translated at a right angle to the beam axis. By rotating the probe it is possible to eliminate the contribution form charge exchange ions and to estimate the mean free path of the energetic ions. The beam intensity is expressed as a polynomial in cosine to the angle between the ion track and the beam axis and we derive mathematical equations to describe the result in distribution of ion current density on a flat and on an umbrella shaped substrate holder. A grid of target points is introduced immediately in front of the holder an in turn we aim the ion gun towards each of these. In each case, we calculate the mean ion current density and the variance across the rotating substrate holder. Finally, we use the obtained maps to optimize the orientation of the ion gun.

Films of Ce-V mixed oxide were deposited by reactive r.f. sputtering from a target of cold pressed CeO₂ and V₂O₅ mixed powders. Optical and ion storage properties of the films have been studied in function of the oxygen partial pressure inside the sputtering chamber during the deposition process. Li intercalation was accomplished electrochemically. Optical constants have been determined for as-deposited and intercalated films.

Thermochromic VO₂ thin films have been deposited by reactive RF cathodic sputtering, using a V₂O₄ target. They were characterized by XRD, AFM and optical measurements. We show that the microstructure influences the optical response of the material, i.e. its hysteresis cycle as well as the values of the optical constants n and k. We performed ellipsometric measurements from the UV to the far IR, combing two kinds of ellipsometers, in both the dielectric and the metallic states. The n and k constants are described by a dispersion law based on Lorentz oscillators, and an additional Drude contribution for the metallic state. The results are confirmed by XPS analysis. Contrary to the semiconductor phase, the metallic phase appears to be strongly dependent of the microstructure, as far as the optical response is concerned.

Zero transmission and very low reflection can be obtained on the whole visible and near IR ranges with a metal-dielectric stack deposited on a transparent substrate. In this case, high absorption occurs within the bulk of the multilayer. Calculation shows that two materials are sufficient to have expected broad-band properties when the metal is associated with a low index dielectric. Suitable design is reached with a eight layer stack including a medium reflectance metal. The total metric thickness of this multilayer is about 0.5 micrometers . Thus this optical coating is convenient for space microbafflers involved in detector arrays or other applications in the field of parasitic light. Electron Beam Deposition process was used to fabricate these metal- dielectric components. Experimental results are presented. They show an absorption around 0.995 in the whole visible range. The achromatic behavior is successfully performed. With a modified design, we can enhance absorption in narrower spectral ranges. Much higher values of absorption are then reached and presented in this paper.

The technology of producing interference coatings for nonlinear crystals has some peculiarities depending on certain properties of such crystals. Besides, the otpical properties of these coatings depend on laser beam irradiation, temperature, and intracavity or extracavity conditions. Temperature in the vacuum chamber, reactive gas pressure, energy of charged particles, conditions of evaporated materials influenced not in the same way as on usual substrates. It was noted that the ion beam acted on pure surfaces of crystals improving adhesion and reducing mechanical stress of the dielectric film. The ion beam sources were used for pre-cleaning just before deposition as assistance in the deposition process. Adhesion, mechanical stress and laser damage threshold depend on the ion beam energy. The optical properties of pure and coated crystals were tested in relation to the ion beam energy. The threshold has been defined. Besides, the degradation of films has been investigated after exposure to the laser beam. Undoubtedly, the antireflection coatings are of the most interest for such crystals. In this work the following aspects of the Ar coatings have been considered: (i) calculation of the optimum construction of optical coatings for a specific spectral range; (ii) production of the required parameters of the films; (iii) study of the optical parameters; (iv) influence of the ion beam on the spectral characteristics of the AR coatings for LBO and BBO crystals. It was noted that only monoenergetic low-energy beams can improve the optical properties for these crystals having AR coatings. As a result of this work, the AR coatings have been produced at one, two or three wavelengths simultaneously.

Fizeau interferometers are traditionally used to determine the surface figure of uncoated optics. Since the reflectances from the uncoated reference and test surfaces are usually equal, the intensity of the interference fringe minimum is zero, so the fringe contrast is unity. If the same reference surface is used to measure the figure of a higher reflecting surface, the fringe minimum intensity is no longer zero and the fringe contrast decreases, eventually reaching zero for 100 percent reflecting optics. The problem can be overcome if the reference surface is coated with a lossy reflecting surface. We describe a coating to measure the figure of optical components having reflectance from 100 percent to 3.5 percent at 1064 nm. The spatial variations across the 150 mm working aperture in physical thickness of the two materials used to coat the reference surface were determined to an accuracy better than 1 nm using a single wavelength ellipsometer operating at 633 nm. Variations across the aperture of the phase changes on reflection from both sides of the reference flat substrate and on transmission were estimated. These results are presented together with calculations designed to determine the relative positions of the outside of the coating with respect to substrate surface as well as the position as seen optically. Substrate distortion due to stress in the coatings has also been measured.

The mechanical behavior of fluoride single layers and thick model layer systems were carried out ex-situ after deposition at laboratory conditions. The samples on substrates with different thermal expansion coefficients have been prepared by a low loss evaporation process. Investigation were performed for single layers deposited at different film thickness, substrate temperature and storage time. All investigated fluorides posses tensile stress of various amounts. The thermal stress component seems to be the major contribution to the total stress MgF₂ films of about 100 nm thickness deposited onto silicon substrate. The stress and force per unit width of model multilayer systems formed from different fluorides were examined and correlated to the ability of crack formation on thick rigid fused silica substrates. Optimization of the stress values, the bending force and the crack formation was performed by adjusting the deposition temperature and by introducing a third stress reducing material in the stack. An example of a stress optimized high reflector will be shown.

Stress in dense thin films deposited by Reactive Low-Voltage Ion Plating or by Ion Assisted Deposition is investigated in air and at room temperature. Ion implantation, at high energy, proves to be a way to vary and diminish the stress in thin films. Stress changes with annealing show the possibility to reducing not only stress but also optical absorption.

In this paper, we report on our investigations of radiation induced processes in optical interference coatings for 193 nm applications with respect to the microstructure of the coating. Experimental studies revealed that fluoride coatings contribute the main source for radiation induced optical changes during its exposure to 193 nm laser irradiation due to their porous microstructure. NIR spectroscopy could identify the origin of optical changes in interference coatings as a reversible hydrocarbon contamination which occurs within the coatings from storage in air atmosphere. Additionally, Laser Induced Damage Threshold measurements show a direct influence of the hydrocarbon contamination on the radiation durability of the multilayer systems during laser exposure. Experiments were carried out by using several characterization techniques including DUV spectrophotometry, ATR-IR-spectroscopy, x-ray diffractometry, and the determination of the '1-on-1' laser induced damage threshold. Test methods were applied to DUV coatings before and after exposure to 193 nm radiation with irradiation doses of up to 10⁸ laser pulses at a fluence of 70mJ/cm². Test samples consisted of several coating designs, primarily of high reflective multilayer systems.

Ellipsometers based on four-detector photopolarimeter (FDP), where the polarization of the reflected beam is characterized in terms of the Stokes vector, have been recently developed and employed as in situ diagnostic of thin film growth. Two main problems are still open. The first is the accuracy of alignment of the FDP with respect to the incident beam, the other concerns the extension of FDP to spectral applications. The base of the set-up proposed in this work is a grating photopolarimeter where a diffraction grating is use data normal incidence and two couples of detectors are arranged in the direction of the diffracted beams corresponding to the +1 and -1 orders. The working spectral range can be chosen by selecting a proper grating. The zero order is used for the autocollimation allowing accurate alignment. For this preliminary study we used a 2 mW HeNe laser as light source. The results of analytical study of the device, its computer simulation, and the examples of application to the ellipsometric measurements of thin films and bare surfaces are presented.

Recently a new approximation for the ellipsometer angles of a slightly inhomogeneous thin film was developed. This approximation enables performing a more detailed qualitative analysis of ellipsometric angles than the widely used approximation assuming the linear bulk inhomogeneity. In particular, the new approximation describes not only the impact of inhomogeneity on the ellipsometric angle (Psi) but also its impact on the ellipsometer angle (Delta) . This paper reports specific properties of ellipsometric spectra connected with the surface micro-roughness. In the particular case of fluoride films the ellipsometric angle (Delta) turns to be quite sensitive to this type of inhomogeneity if ellipsometric measurements are performed at high angles of incidence.

Spectroscopic ellipsometry has become one of the most powerful tools of the investigation of the optical properties of thin films. In this paper we show that it enables one to successfully detect even fine properties of high-quality thin films, such as small bulk and surface inhomogeneities. In our experiments, niobium pentoxide films were deposited by ac magnetron sputtering on to quartz substrates with a thickness approximately equal to 500 nm. A J.A. Woolam variable angel spectroscopic ellipsometer was used to measure the ellipsometric parameters of the films over a spectral range from 400 nm to 850 nm. The measured ellipsometric data obtained at the different incidence angles were then analyzed using the OptiChar characterization software. All measurements indicated the presence of a surface micro-roughness in the film, estimated to be around 1 nm. This surface micro-roughness was modeled by a surface overlayer with a 50 percent packing density. The films also possess a small positive bulk inhomogeneity on the order of about 1.5 percent. In the specific case of Nb₂O₅ films on a quartz substrate, the ellipsometric angle (Psi) at a 65 degree angle of incidence is the most sensitive to surface and bulk inhomogeneities. The presence of inhomogeneities of both types is clearly seen at certain wavelength points.

Mixed oxides are useful for obtaining the intermediate refractive indices needed in the realization of graded-index thin films. Co-evaporated TiO₂-SiO₂ mixtures are studied for a large range of concentrations via UV-VIS, IR ellipsometry and XPS. An understanding of the nature of these mixtures and their air exposure stability is important for further applications. At low TiO₂ concentrations, Ti⁴⁺ ions are inserted into the silica tetrahedral network, as shown by the IR peak at 945 cm^-1. At higher concentrations, an evolution from TiO₄ tetrahedra to TiO₆ octahedra is presumed. The behavior of the O_1s core level peak indicates that a least two phases coexist. Comparison between concentration determined using XPS and RBS shows a deficit in TiO₂ at the surface of the films, especially at high TiO₂ concentrations. The evolution of the mixtures optical constants will be presented in a large wavelength range, going from IR to UV. Particular attention will be paid to the variations with respect to the frequency of the vibration modes in the IR range, to the refractive index in the transparency region, and to the extinction coefficient at he absorption threshold. In addition, AFM measurements show the variation of the grain size as a function of the TiO₂ concentration.

The knowledge of the statistical and spatial distributions of optical absorption and scattering can give precious information about the size and the event frequency of the defects which may play an important role in laser damage for examples. The surface size to be characterized depends strongly on the application. A high spatial resolution is necessary to study micro defects while large areas have to be scanned to check the whole sample. In this paper we are interested first in multiscale studies of losses. We present some results in which we have changed the explored spatial window while keeping constant the spatial resolution. Furthermore we have tested the lateral spatial resolution of absorption mapping by photothermal deflection. A 5 micrometers - pattern with a high absorption contrast can be displayed by using a pump beam of 10 micrometers and a sampling step of 5 micrometers in spite of a probe beam of 28 micrometers . We have obtained the same result with a 3 micrometers -pattern of low absorption contrasts by using a pump beam of 3 micrometers and a sampling step of 2 micrometers . These experiments show that the spatial resolution is determined in a rough approximation by the pump beam diameter.

The progress in the design of optical coatings is essentially connected with the invention of the needle optimization technique and with the accumulated experience of its practical implementation. These factors enable raising a question about the developing of an entirely automated optical coating design technique. The presented paper discusses difficulties of the formalization of the design problem and the ways to overcome the intrinsic uncertainty of its formulation. It formulates the basic principles of implementation of the entirely automated design technique and considers the main pro et contra of the push-button design technology.

The needle optimization technique is applied to the designing of broadband coatings with simultaneously specified intensity and phase derivatives targets. Specifically the designing of output couplers with the transmittance equal to 6 percent in the spectral region form 650 nm to 1100 nm is considered. Other targets include group delay dispersion upon transmission (GDDT) and group delay dispersion upon reflection (GDDR). Theoretical considerations exposing the nature of GDDT and GDDR oscillations are provided.

Normal-incidence multicycle broadband AR coatings on glass with low residual over the wavelength region 400 nm to 800 nm are theoretically discussed. Using the method of effective interfaces and the concept of equivalent index layers a 4-layer design sub(AHBL)air is expanded into the designs sub[AH(C2LC)²BL]air where A, B, C, H, and L are quarter-wave layers with refractive indices n_H equals 1.38, n_L equals 2.35, and n_L < n_(Lambda ), b_B, n_C, < n_H. These designs represent 1-cycle, 2- cycle, and 3-cycle broadband AR coatings and perform a residual reflectance of 0.20 percent, 0.14 percent, and 0.10 percent, respectively. Four other designs demonstrate the approach at other wavelength regions. In one example, all quarter-wave layers with refractive indices in-between n_L and n_H are analytically substituted using equivalent index layers to get two-material multilayers suitable for practical applications. After this, the design is refined with respect to the optical thickness whereby the layer number is fixed. The resulting design consists of 18 layers and performs an average residual reflectance 0.085 percent over the region 400 nm to 800 nm.

A new automatic method is proposed for the design of thin- film optical coatings. The principle of this method consists in increasing gradually the layer count of a coating by adding thin layers at one end of the design. Each time a new layer is added, the design is optimized. However, this optimization is performed using an external medium whose refractive index corresponds to the index of the next layer to be added. This procedure, for which the external medium is regularly alternated, first degrades the optical properties but permits to improve them afterwards, while this may not be possible using the real external medium of the design. This real external medium is only taken into account at the end of the synthesis work. A major advantage of this method is that the starting design can be restricted to the list of materials used both for substrate and layers. No starting thickness is required. An other advantage is that the final layer count of the design does not seem limited.

New technology applications require new types of x-ray mirrors, in particular, mirrors working at different grazing angles. The angular range of standard x-ray mirrors is rather narrow and they cannot provide effective collimating and focusing of x-ray beams. It is shown that the needle optimization technique can be effectively applied to the design of x-ray mirrors with an extended angular range. Experimental results confirm a practical reproducibility of the designs obtained using this procedure.

A numerical procedure for solving the effective medium approximation equations for ellipsometric data analysis is presented. The idea is to transform the complex root-finding problem into a minimization task in real space. Thus, the method can be implemented through a standard downhill simplex algorithm, leading to a general, simple and useful technique for ellipsometric developments.

Equiripple bandpass interference filters are designed by the refinement of a few layers of standard QW multicavity designs, and some simple manipulations of the solutions. Ways to control the intermediate refractive indices of the running layers, and/or their non-QW optical thickness, are described. Some limitations of earlier approaches are avoided.

Light scattering is well known to be a key limitation of the ultimate performances of filters. Whatever the values of surface roughness and bulk heterogeneity within the multilayer, the optical losses depend on the stack design and on the correlation factors between defects. Such situation is largely enhanced in the case of WDM filters, due to the high over-intensity of the electric field within the stack, as a consequence of the narrow pass-band. In this paper, we present some experimental scattering result recorded with a high angular and spectral resolution on prototype WDM filters and which illustrate the enhancement of scattering near the design wavelength of the filter.

Spontaneous emission control for rare earth ions implanted inside planar multidielectric microcavities is presented and compared in order to compute the electromagnetic power provided by sources locate inside planar dielectric multilayer structures. Radiation patterns are measured in Ta_{2$.O(subscript 5}/SiO₂ microcavities implanted with praseodymium ions. Although we demonstrate a significant enhancement of the spontaneous emission in a direction normal to the layer, we show that a large amount of the emitted power is carried by the guided modes of the structures. As a direct application for thin films auto- fluorescence modifications, we concentrate on visible dielectric thin film luminescence under UV irradiation for the high index/low index couple HfO₂/SiO₂. We exploit those result in an attempt to understand the proper luminescence of three different mirror stacks, both in terms of luminance efficiency and angular emission. This study introduces the 'luminescence engineering' concept which may appear as a relevant thin films design criterion for biological applications.

In the context of new generation of Earth observation satellites, and supported by CNES REOSC has developed new kinds of interference filters placed just in front of the detector lines. Usual spectral bands B1 B2 B3 for visible and near IR range are selected separately on the same substrate by three different multidielectric coatings. Each coating forms a line of 80 millimeters length and 50 microns width, two consecutive and parallel filters being separated by 200 microns. Between each line and all around them on the total surface of the substrate, a black coating with absorbing and antireflective efficiency prevents straylight to reach the detector. The full process of manufacturing uses successive coating and engraving technics which ensure extreme precise positioning of each filter with less than 3 microns tolerances. Spectral performances go up to 85 percent of global transmittance in each spectral band and less than 1 percent of integrated rejection al over the detector sensitivity range. The spectral characteristics of these steep edges bandpass filters are completely insensitive to air-vacuum transitions and the component support with success all qualification sequences of space environment.

Fresnel lenses for projection optics require a reduction of reflection losses in a wide wavelength and angular range. Their surface relief consisting of inclined microstructures with increasing inclination angle causes a reduction in AR- coating thickness form center to the edges and hence a spectral shift.

Refractive index gratings made by titanium ion implantation are studied. Computations using the rigorous differential method and otpical measurements show that our gratings implanted in SiO₂ substrates have a diffraction efficiency of typically 2 percent in the 1st order. We propose to insert such grating in multilayer dielectric Fabry-Perot cavities in order to enhance the free space diffraction efficiency. Computations are performed by taking into account the index profile of the implanted zone. The best structure is obtained by optimizing the thickness of the implanted silica layer which is embedded between two mirrors. We study the dependence of optical properties of the structure with respect to various characteristic parameters such as the index profile, the multilayer design, the filling factor of the grating and the incident angle. To demonstrate the feasibility of such components, we focus our attention on an implanted grating embedded in a Fabry-Perot cavity whose mirrors have five dielectric layers. This component reaches a theoretical efficiency of 10 percent in the 1st order. First experimental results are presented.

Electron-beam deposition is the current method to produce large-aperture high laser-induced damage threshold coatings for the National Ignition Facility, a 1.8 MJ fusion laser. The e-beam process is scalable to large optics up to 0.25 m² and with laser conditioning has relatively benign coating defect ejections resulting in high damage threshold thin films. The latest technological breakthrough in manufacturing high damage threshold coatings is e-beam deposition of hafnia by evaporation from a metallic instead of an oxide source in a reactive environment. Although the damage threshold is not significantly increased, a 3-10x defect reduction occurs resulting in significantly less coating modification during laser conditioning. Additional benefits of this technology include improved interfaces for the elimination of flat-bottom pits and up to 3x reduction in plume instability for improved layer thickness control and spectral performance.

High power lasers at 1.06 micrometers wavelength like the French 'Megajoule' program require large area mirrors made of alternative layers of HfO₂ and SiO₂ with high damage threshold. It has ben already identified that nodular defects have a significant role in the activation of laser damage. The purpose of this paper is to study experimentally the role played by the size and the nature of the seed on the critical behavior of the nodular defects under laser irradiation. Artificial nodules have been grown with careful control of location and seed size. these nodules have been generated with diamond and silica seeds. Silica seeds of four different sizes have been used. A method which minimizes clusters of particles has been successfully used. With this method, we have obtained defects with a sharp size distribution. These samples have been tested on our automatic damage test bench in various modes. The thresholds between polluted and unpolluted mirrors are discussed according to the size and the nature of the seeds. The damage sites are observed with a scanning electron microscope. These experimental results are compared with a damage model.

SiO₂ and HfO₂ thin films have been deposited on polished fused silica substrates by the ion assisted electron beam evaporation technique in different deposition conditions. The role of the assisting ion beam parameters either on the otpical and structural film properties and the film damage threshold at 308 nm has been investigated. Laser damage thresholds have been determined by the photoacoustic mirage technique.

The electric field magnitude and profile influence the laser-induced damage threshold and morphology of a multilayer coating. Through the use of non-quarter-wave layer pairs in high reflector designs, the electric field peaks are shifted into the low index layers thus reducing the electric fields in the high index layers and interfaces. Similarly the electric field profile in a polarizer can be optimized for low electric fields within the high index layers and film interfaces by proper design selection.

Storage Ring Free Electron Layers (FELs) are brand new laser sources where a relativistic electron beam passing through an undulator emits synchrotron radiation at a wavelength (lambda) which is tunable according to the electron beam energy and the magnetic field intensity. An overview of the SRFELs presently operating in the UV range is presented. The easy tunable FEL operation in the whole UV range is mainly limited by the mirrors losses, which should be maintained low even in the very hostile environment generated by the broadband high power spectrum of the undulator, extending to x-rays, and which action lead to the mirrors degradation. Dedicated mirror measurements have been then developed in LURE, in the visible and in the UV range, for checking the mirrors performances before insertion in the optical cavity and after degradation. In order to insure a wide tunability range and large output power of the FEL, low total losses are crucial for FEL oscillation at shorter wavelength. New FEL sources, for instance at the ELETTRA synchrotron source, could then provide a widely tunable and powerful laser light down to 200 nm.

The OSIRIS camera system on board the ESA Rosetta mission to comet 46P/Wirtanen will carry interference filters with glass substrates. During the long cruise phase the probe will be immersed into an environment of energetic particles, especially when the trajectories of solar coronal mass ejections will be traversed. We have studied the effects on the transmission curves of clear and colored glasses of such MeV proton bombardment, using laboratory simulations covering the expected range of fluence. As a result, while Quartz Suprasil glass was radiation hard for all considered does, Schott OG590 and KG3 glasses showed reductions in transmission up to 5-10 percent though only for doses exceeding the expectance for Rosetta. Furthermore, about half the effect was annealed away at room temperature with a time constant of the order of one day.

The obtaining and investigations of interference coatings in deep ultra violet at 193 nm for medical applications are considered. For successful using in excimer medical system each optical elements must have anti-reflective or high- reflective interference coatings that can be satisfied to medical setup. The general problem is how to produce the event distribution of primary laser irradiation at the nearest distance from eye behind the optical system with minimum losses. Besides all types of coatings must provide a high strength under laser irradiation. The conditions of producing interference coatings in this spectral region have some peculiarities: a limiting factor of the evaporation materials, film homogeneous along the surface of optics, and high laser strength. The processes of interaction between excimer laser photons and optical coatings influenced both on substrate and on film. In this connection the optical properties of some evaporated materials and pure substrates are observed. All films were produced by electron-beam evaporation. Optical absorption and laser strength of coated optics was analyzed as influence and variations of energies of ion-beam source.

For many applications, reducing the total amount of the light scattered from rough surfaces is a crucial problem. We show that a scattering-reduction effect is obtained by coating rough absorbing surfaces. Numerical results as well as experimental ones are presented. We also study the case of inhomogeneous structures with embedded scatterers.

Total integrated scattering (TIS) and bi-directional reflectance distribution function measurements give information on the mean roughness of the surface and on the modulus of the Fourier Transform of the 2D surface profile. To obtain a more precise description of a rough surface and to get an estimation of the relative contribution of surface and volume scattering in multilayers stack, we have developed a new interferometric method which allows us to measure the variation of the phase of the Fourier Transform of the surface profile as a function of the scattering angle. This paper includes a detailed presentation of this method, a description of the experimental set-up used for its principle validation, as well as some preliminary results that we have obtained with it on high reflectance samples.

This film roughness and its correlation with the substrate microtopography are studied using x-ray scattering at (lambda) equals 0.154 nm. The approach is applied for the investigation of superthin films of several nanometers thickness, when both interfaces are responsible for x-ray scattering, and consists in the direct determination of PSD functions from a set of x-ray scattering diagrams measured at different grazing angles of the probe beam. X-ray scattering methods are demonstrated to enable the quantitative evaluation of PSD functions of external film surfaces as well as the correlation between the substrate and film roughnesses. Results of measurements of thin films of materials widely used in the fabrication of short-period multilayer mirrors are discussed. The result of the x-ray scattering measurements are compared with independent investigations of the external film surface by atomic force microscopy.

Oxide single layers of niobium oxide and silicon dioxide with different film thicknesses and multilayers consisting of this both components were deposited by reactive sputtering on silicon substrates. The loss of optical performance by structural imperfections was characterized measuring the total light scattering in comparison to AFM roughness investigations. The measured scattered light and the rms roughness values calculated from the AFM images were found to correlated clearly with the density of macroscopic defects in the Nb₂O₅ and SiO₂ single layers. With multilayers, similar effects were observed.

It has been shown that measuring the polarimetric phase of the field scattered from a thin film multilayer gives information on the origin of scattering. Numerous numerical simulations have shown that the behavior of the polarimetric phase can be used to separate surface and bulk scattering. In the case of stacks with correlated interfaces the polarimetric phase depend only on the origin of scattering, whatever the microstructural parameters. Slight deviations from vertical correlation within the stack lead to ripples in the polarimetric phase, that can be observed experimentally. Moreover in certain cases second order effects, due for example to localized defects, can lead to depolarization. This phenomenon has strong influence on the polarimetric phase. This can be used to detect contamination of the surface. In our communication we will present some experimental results that show that the origin of scattering can be determined.

Optical thin films are nowadays major obstacles in deep UV lithography. Scattering and absorption losses are the dominant factors which limit their optical performances. The reduction of scattering requires the development of specific deposition techniques. As a new way of manufacturing optical thin films for 193 nm applications, we applied Ion Beam Sputtering (IBS) to fluoride coatings previously developed for 355 nm. In order to check the ability of IBS to reduce the scattering losses of coatings, various quarterwave and halfwave coatings as well as multilayer stacks deposited onto fused silica and CaF₂ substrates were produced and characterized by total scattering (TS) measurements at 193 nm. An AFM was used for direct imaging of the surface features and calculation of rms surface roughnesses. Subsequent data processing provided power spectral density curves containing more detailed roughness information. The evolution of the surface roughness and scattering with increasing film thickness or number of layers was analyzed and the results were discussed in order to determine the origin of the scattering and to highlight the benefits which can be expected from IBS processes.

For a large number of specific applications, optical materials must be used in powder forms. In this context it has become highly necessary to characterize the optical and microstructural properties of such powders. Preliminary scattering experiments have shown that the scattering intensity from materials in powder forms could be quite different than that of the same homogeneous materials. In particular we have noted a strong increase in the level of the scattered light that could come from the bulk scattering. Here we show how to use the light scattering techniques in order to separate and determine the roughness and inhomogeneities of the samples. The same techniques are used to determine with accuracy the refractive index and absorption of the powders. In a second step, the same powders are evaporated in thin film forms, and we use classical spectrophotometric techniques to determine their refractive index and dispersion laws. The result are compared and discussed with those obtained with light scattering. In a general way, this study involves surface and bulk theories of light scattering, together with angle- resolved measurements, and atomic force microscopy.

In high quality otpical coating systems for the DUV-spectral range, MgF₂ is one of the preferred deposition materials. MgF₂-coatings exhibit relatively low optical losses as well as high stability and laser induced damage thresholds. In the present joint research effort of several European laboratories, the potentiality of MgF₂ is evaluated in respect to the production of improved optical coatings for applications in laser technology and semiconductor lithography. For this purpose, single layers of MgF₂ were deposited on superpolished fused silica and CaF₂-substrates by ion beam sputtering, boat and e-beam evaporation in different laboratories. Besides photometric inspections, the samples were characterized by an optical scatter measurement facility at 193 nm and 633 nm. The structural properties were assessed using AFM, XRD, and adapted TEM-techniques invovling conventional thinning methods for the layers. For the measurement of mechanical stress in the coatings, special silicon substrates were coated and analyzed.

Zeeman laser gyros have found wide application. Contrary to ordinary laser gyros operating at linear polarization of emission, Zeeman gyros require the use of mirrors having low losses in both polarizations at oblique incidence of laser emission and minimum phase anisotropy. High-reflection TiO₂ and SiO₂ mirrors at 632 nm for such gyros have been produced by ion-beam sputtering for the angle of beam incidence of 45 +/- 1 degree. The characteristics of the optical coatings have been measured by laser modulated photothermal radiometry, photothermal deflection technique, total integrated scattering measurements, the resonance method using the ring cavity, and the ellipsometrical method. The obtained results have allowed optimization of the coating deposition processes. For the 23...25-layer mirrors the following results have been obtained: (i)absorption - 30...70 ppm; (ii) total integrated scattering - 50...70 ppm; (iii) total loss - 250...300 ppm in circular polarization; (iv) phase anisotropy of p and s components of emission - 0.03...0.05 rad. The produced mirrors have allowed realization of compact Zeeman laser gyros with a lock-in about 100...200 Hz and an accuracy of angular velocity measurement at a level of 0.1 degree/h. The ways to reduce the ion-beam mirror losses are discussed.

Indium tin oxide (ITO) thin films were prepared by unipolar and bipolar dc-pulsed magnetron sputtering in a mixture of argon and oxygen onto the unheated glass substrates. The target of ITO with 10 weight percent tin is used. The influences of polar modes, output frequencies, and on times and off times on the optical, electrical and structural properties of ITO films are investigated. The correlations between the deposition parameters and the film properties are discussed. An optimal condition based on the polar mode and frequency of reactive dc-pulsed sputtering for obtaining the high transmittance and low resistivity of ITO films is suggested.

Deposition rate during laser evaporation is about 3-5 times higher than during thermal evaporation. Evaporated malonitrile-based merocyanine (Mc) and phtalocyanine (Pc) dyes from smooth films with high optical absorption and reflection in visible and near-IR regions. PcVO film, deposited at 20 degrees C consists of high temperature crystal phase. Co-deposition of polymer and dye showed that the films consists of the polymer matrix filled by dye nanoparticles. Polystyrene and polychlorotrifluoroethylene were used. It was known before, that low temperature plasma treatment of some dye vapors led to their polymerization and stability enhancement, but specific optical properties were reduced strongly. We tried to adjust dye chemical structure and plasma parameters. Films enhance their adhesion and stability significantly, retaining high optical absorption. Their spectra have some peculiarities, but main peaks are the same as for the parent dye.

Thin metal-filled polymer films produced by low temperature plasma are used as resistors, protective coatings, catalyzers. Among the others they are used for optical recording media. The possibility to use MOC PECVD for optical recording media production using the Te-based precursors was shown. Sb-based metal-polymer films also attract attention before because Sb is less toxic and more stable, than Te. In this work authors used plasma polymerization with simultaneous Sb evaporation forma boat. In the researches known before the precursor dissociation during PECVD is carried out mainly by low frequency, radio frequency and microwave discharges. Each of these discharges have peculiarities which result on film properties. But all these discharges effect on both dissociation and polymerization processes, which leads to difficulties to obtain films with predetermined properties. It was known before, that the pulsed discharge use for polymerization of organic monomers allows to rule of the ratio between dissociation and polymerization processes, what effects strongly films properties.

Cathode sputtering is a well-known technique for deposition of thin films starting from metallic or ceramic materials. Ceramic insulating materials are usually sputtered using radio frequency as electric power source. In this work we compare the optical properties of tin films deposited from two different types of targets. The first set of samples was deposited from solid targets glued to a water-cooled back- plate. For the second set we used targets made of cold pressed powders of the corresponding materials. The possibility of sputtering from weakly pressed powders can be favorably exploited to develop mixed materials. Their cost, in fact, is about one tenth of glued solid targets, and mixtures of any required composition can be quickly prepared. Two oxides, SiO₂ and Al₂O₃ have been deposited by both methods in the same deposition chamber, using the same process parameters, and sputtering gas. Their optical characteristics - refractive index and extinction coefficient - have been compared over the VIS-NIR spectral range.

The aim of this work is to check the possibility of using originally developed thin films of mixed oxides of cerium and vanadium as ion storage electrode within an electrochromic cell. Transmittance variation as function of the amount of lithium exchanged between the WO₃ film and the Ce-V oxide film has been measured in the visible and near IR spectrum. Also real time single wavelength measurements have been performed in different conditions to test the speed of coloration.

Classical narrow-band interference dielectric filters with all-dielectric reflectors have the quarter-wave stacks separated by a half-wave thickness spacer layer. These filters are essentially the Fabry-Perot filters and hence the theory developed for the latter applies in full. The paper present the theory of narrow-band interference dielectric filters with non-conventional spacer layers. This spacer consists of the layers of two different materials. The optical features of these filters are compare with the features of Fabry-Perot filters. It is analyzed the influence of the errors of layer on spectral characteristics. Presented theory may be applied to any spectral ranges as well as to any thin film materials including absorbing and nonlinear materials.

The temperature of a nanosatellite in orbit varies strongly as it goes into earth shadow or solar radiation. A variable emittance panel built with an electrochromic material, could improve the temperature control by providing an adaptive thermal control. The active function is due to an electrochromic layer, WO₃, deposited by sputtering. Intercalation of Li⁺ leads to a change in the electron configuration, which modulates the radiation properties. Thin WO₃ films were deposited onto Indium Tin Oxide (ITO) coated glass by reactive dc sputtering. IR measurements were done in a Perkin-Elmer 983 spectrophotometer. The IR emittance modulation, (Delta) (epsilon) of WO₃ films, deposited on ITO coated glass, has been investigated. The emittance, (epsilon) , is computed from the reflectance, at 25 degrees C. Initial results show emittances in the range from 0.2 to 0.5 crystalline film has (Delta) (epsilon) equals 0.12, and the amorphous film has (Delta) (epsilon) equals 0.3. IR properties of WO₃ need to be further investigated as well as the construction of a whole device.

Thermal control is an important issue in small-scale satellite design, and thin film coatings suit the limited mass and volume constraints. Group IVB transition metal nitride films meet the criteria that the satellite surface must be mechanically and chemically stable, and electrically conducting. Thin film Ti_xAl_yN_z coatings have been investigated and tailored for temperature control. The films were deposited by reactive sputtering on aluminum substrates in N₂/Ar-atmosphere. The solar absorptance, (alpha) , and thermal emittance, (epsilon) , were calculated from spectral reflectance measurements. It was found that an optimization of film composition leads to a reduced equilibrium temperature. The composition temperature. The composition Ti_0.16Al_0.41N_0.43 has a flatter reflectance curve than TiN, and was found to be close to optimal. By varying the film thickness, interference effects could further reduce the equilibrium temperature. A 650 nm Ti_0.16Al_0.41N_0.43 film showed a reflectance interference minimum positioned at the maximum of the blackbody spectrum, resulting in an increased emittance. Neglecting internal heat contributions, the lowest calculated equilibrium temperature was 34.6 degrees C for this film.

Miniaturized interference filters were designed and fabricated using three different manufacturing technologies. Applying micro-milled ceramic masks during the coating processes different arrays of interference filters with 1 mm lateral feature size were arranged on a 3-inch Si-substrate. The spectral sensitivity of receiver cells has been modified by direct coating using ion assisted deposition (IAD) at low temperature. IAD-processes also allow the application of microlithographic masks, which are removable by organic solvents after the deposition process. As an example three different miniaturized interference filters were arranged side by side with lateral filter dimensions of a few tens of microns. A combination of coating processes, microlithographic masking procedures, and reactive ion etching made it possible to arrange three different stripe filters with minimum filter features of about 5 micrometers side by side.

Most Fresnel lenses for projection systems are made from Polymethylmethacrylate (PMMA). Such lenses, e.g. for LCD- projectors, are flat discs whereas one surface is plane and the other microstructured. Special coatings are necessary to reduce stray light and 'hot spots' in the projected image, finally. Plasma-ion Assisted Deposition has been applied to realize dielectric multilayers on PMMA. Additionally, a low pressure plasma pre-treatment has been carried out as the first step of the coating process which inducing an irreversible modification of surface composition that leads to excellent adhesion conditions for coating. The special problem for coating the microstructured surface is the inclination angle of the small Fresnel facets which increases from the center to the outer area of microstructured lens. Consequently, the vapor incidence angle changes in the same way. Another problem is to keep the temperature at the polymer surface low during coating process. Thin microstructured polymer lenses show lower dimensional stability compared to flat or compact samples. Several coating designs have been invested to get a uniform moderate antireflective effect and in result an optimized light impression for the observer.

In contrast to 'conventional' algorithms for determining the otpical and geometrical characteristics of interference coatings, we present an alternative approach using artificial intelligent systems for reverse search tasks. The goal is to develop a neural network which is able to distinguish characteristics spectral features of optical thin films, such as specific interference pattern as well as absorption lines or edges. We demonstrate the application of neural networks to determine film thickness, refractive index and surface roughness of a thin film from the interference pattern of the specular reflectance spectrum in the near IR. For simplicity, in this case both film and substrate materials were assumed to be free of absorption losses. Such tasks may be solved using considerably simple neural networks containing up to 52 neurons for 128 spectral points. Current activities include the extension of the method to absorbing thin film system. We particularly emphasize the significance of a mathematical pre-processing of the spectral data in order to keep the network dimensionality as low as possible. Basing on the first result we strongly suggest that neural networks may be successfully applied for fast estimation of thin film thickness, roughness and optical constants and may consequently supply reliable initial values for any subsequent local minimum search procedure.

The deposition of gradient index coatings attaches a higher importance for science and also for industrial applications. Especially the progress in chemical vapor deposition technologies opens new opportunities for the production of various types of gradient index coatings. However, the characterization of these types of coatings plays a substantial role in the optimization of coating processes.

To grow dense and hard MgF₂ films substrate temperatures of about 300 degrees C are required, which unfortunately leads to high tensile film stress and the ability of crack formation. Lowering tensile stress in MgF₂ films can be achieved by admixture a second fluoride material of higher cation radius than Mg²⁺. While former investigation were performed with non-heated films the purpose of the present work was to verify the behavior of mixed films when deposited at elevated substrate temperatures. One of the promising add material is BaF₂ which enables evaporation of appropriate pre-mixed materials from a single source. The BaF₂ content in the mixed films was varied from 3 to 55 mol percent in the MgF₂ host. Optical, mechanical, and structural properties of samples deposited at different substrate temperatures have been studied by spectral photometry, IR spectroscopy, ex situ measurement of mechanical stress, x-ray diffraction, and -reflectometry, RBS, as well as investigation of surface morphology.

A constrained optimization design procedure is described which gives good control of the spectral position of a filter edge and simultaneously optimizes pass band transmittance. The underlying principle of our previous study was to use constant level monitoring and position that constant layer termination photometric level for the least sensitivity to photometric and other layer termination errors. Additional layers are needed between the substrate and the periodic stack to bring the layer termination to the ideal level and also provide the antireflection coating of the pass band of interest. The requirement can be stated as: the preliminary layers must move the reflectance phase at the monitoring wavelength from that of the substrate to that of the start of the periodic stack needed for CLM. The constraints are that the magnitude and phase values at the end of the deposition of the preliminary layers satisfy these specific requirements. The constrained optimization can vary both the pre- and post-periodic matching layers while attempting to meet the transmittance targets and simultaneously satisfy the constraints. When this is done, the resulting design has optimized transmittance and satisfies the required constant level optical monitoring conditions for the most reproducible result in production.

Vanadium dioxide undergoes a semiconductor to metal phase transition at approximately 68 degrees C which is accompanied by a marked change in material conductivity and an associated change in optical properties. In order to fabricate devices, which utilize this change of optical property in the IR region of the spectrum, the design engineer requires reliable optical data. High quality vanadium dioxide films have been produced by a reactive magnetron sputtering technique from a vanadium target in an atmosphere of controlled oxygen content. A UHV system was used to ensure very low impurity level sin the deposited films. Quartz crystal monitoring allowed rigorous and reproducible control of film stoichiometry. Various thickness layers of vanadium dioxide were deposited on high optical quality IR transmitting substrates. The optical properties of these films have been determined in both the semiconducting and metallic states. Measurements were made of transmission and specular reflectance using various spectrophotometers. From these measurements n and k and absorption coefficient values were evaluated. These result are reported and compared with the previously published values given for bulk vanadium dioxide. These comparisons show excellent agreement and hence confirm the films are monocrystalline in nature as indicated by x-ray diffraction results.