In the last few years, optical coating design has been projected from a somewhat traditional and slow-moving subject into the foreground of activity. Important sections of conferences are being devoted to it and there is intense competition in the supply of software packages for coating design and analysis. This paper reviews some of the background to design, suggests reasons for the current state of the subject and comments on possible future directions.

A new method is proposed for designing antireflection multilayers, characterized by an assigned number of layers and given materials. It is based on a two-stage Monte Carlo exploration of the thickness space. In the first stage, many thickness vectors are generated with a uniform distribution over several appropriate sub-boxes in the thickness space. The sub-boxes with the most promising results are preserved only. The second stage is self-focusing in each surviving sub-box: here, thickness vectors are generated non-uniformly by taking into account the distribution of the merit figure obtained previously. Finally, the sub-optimal multilayer of each surviving sub-box works as starting design for the final refining. As an example, the synthesis of antireflection coatings is presented for Germanium IR optics in the region from 7.7 to 12.3 micrometers.

The optical transmission properties of a 1D dielectric multilayer filter, realized by a refractive index distribution that follows a Cantor sequence have been studied. Different polarizations are considered. Examples of different kinds of materials are presented.

Modern optical components require sophisticated coatings with tough specifications and the design of optical multilayers has become a key activity of most laboratories and factories. A synthesis technique based on the simulated annealing algorithm is presented here. In this stochastic minimization, no starting solution is required, only the materials and technological constraints need to be specified. Moreover, the algorithm will always reach the final result. As simulated annealing is a stochastic algorithm, a great amount of state transitions is needed in order to reach a global minimum of the merit function used to evaluate the difference between the optical target and the calculated filter. Anyway the computing time remains reasonable on a work-station. A few examples will show the performances of our program. It also has to be pointed out that no refinement is needed at the end of the annealing because the solution is already highly optimized. Nowadays the design of robust filters with low sensitivity to technological variations remains a key factor for manufacturers. This is why we have established some criteria that quantify the robustness of the stacks. It also enables comparison of multilayers synthesized by different methods and corresponding to the same target.

Graded reflectance coatings are typically identified with optical coatings having a gaussian reflectance profile along the surface with circular symmetry. Indeed the first use of such coatings was as output couplers of gaussian laser resonators, then also super-gaussian reflectance profiles were considered. The variation of reflectance along the surface is obtained in most cases by a coating thickness variation, with an appropriate choice of both coating structure and thickness profile it is possible to obtain any maximum reflectance and any spatial behavior of the reflectance itself. New reflectance profiles that seem to be of interest are: graded reflectances with a central minimum, that is high transmittance at the coating center, and non- monotonic radial reflectance profiles as for example high reflectance on an annular area of the optical component. In addition, coatings with non-circular symmetry appear useful for particular laser applications. The methods for obtaining such reflectance profiles are discussed.

According to the maximum principle in thin film optics multilayer designs are optimal at least at the normal light incidence. Nevertheless multilayer designs featuring spectral properties typical for inhomogeneous coatings are not widespread. This is connected with the computational problems related to the design of multilayers with large number of layers. This paper shows that using needle optimization technique it is possible to design multilayer counterparts to rugate filters. These multilayers possess even better spectral properties than their inhomogeneous prototypes.

Infrared (IR) optical systems tend to make use of IR lens and window materials with high values of refractive index, such as germanium, zinc selenide and zinc sulphide. Consequent Fresnel reflection is sufficient to significantly degrade effective transmission and IR imaging capability. To maximize IR optical performance in such systems, Barr and Stroud has for over 20 years produced high efficiency IR anti-reflection (AR) coatings for lenses and windows. Typically these coatings provide average reflectance below 0.25 percent per surface with sufficient durability to meet internal surface environmental conditions. Design constraints on these AR coatings require a low refractive index outer material, with recent technology and practice relying on thorium fluoride to fulfill this role. The main disadvantage of thorium fluoride usage is its associated radioactivity and high toxicity. Moreover, present IR coating requirements insist upon replacement of thorium fluoride with a non-radioactive, low toxicity, low index film material. A research program at Pilkington Optronics (Barr and Stroud) has resulted in the identification and characterization of yttrium fluoride as a suitable non- radioactive replacement film material with reduced toxicity for use in the 3 to 5 micrometer and the 8 to 12 micrometer IR spectral regions. As described in this paper, this material has been successfully incorporated into high efficiency single and dual band AR coatings for germanium, zinc selenide and zinc sulphide, without compromising optical and durability performance.

The deposition of smart-filters like the V-lambda filter demands a precise knowledge of the refractive index at every position in the multilayered thin-film structure, and the ability to control the optical thickness of each layer precisely. The smart-filters produced by us today are soft coated of Zinc-Sulphide (ZnS) and Misch-Fluoride (MiF). The deposition of the complex multilayered structures is controlled by a computer based system collecting data from a transmission measuring system. Special test runs have revealed that the packing density of the ZnS depends on the physical thickness of the undercoat whereas the packing density of the MiF depends on the substrate temperature and the packing density of the undercoat. The substrate temperature that depends on the radiated heat from the crucibles, the speed of deposition and the radiation of heat to the surroundings is predictable when the thin film design is known. The speed of deposition is servo controlled and the time consumption for the coating process stay within +/- 5 percent of the predicted value.

Real time monitoring and control, by multiwavelength phase modulated ellipsometry of the growth of plasma deposited optical structures is presented. The transparent layers consists of SiO₂ SiN_x and oxynitrides. We present an efficient method for the estimation of the optical parameters based on a sliding window containing the last acquired measurements. This method is used to monitor the deposition of multilayer coatings with homogenous deposition conditions, and is also used in feedback control of such coatings. The sliding window method is further developed to follow slowly time-varying parameters such as the deposition rate. A preliminary study of a fast novel method based on the same principle for real time monitoring of refractive index gradients is described. As an example, the real time monitoring of the growth of a linear gradient index is demonstrated.

The words 'black art' are often associated with thin film coating. We cast our spell on a coating plant and, as if by magic, the glass is transformed. The problem is that the spell sometimes fails and we end up with stone instead of gold. When we ask the magician (coating technician) what went wrong, the answer is all too often 'I did it exactly the same way as the last time'. This creates the perception that thin film coating is a black art because clearly something different did happen. What we don't know is which of the multitude of parameters went wrong, and often the only way to find out is through a process of elimination. This is very costly to the industry both in monetary value and image.

An improved plasma source for use with oxygen and other gasses has shown great stability at ion power levels almost an order of magnitude above those of the other commercially available gridless sources. The original motivation of this work was to obtain a powerful a source of oxygen ions with neutralizing electrons (plasma source) for the reactive deposition of SiO₂ from SiO. The results are also applicable to other gasses such as nitrogen, argon, etc., and other deposition materials. The characterization of the source in detail by the use of the design of experiments methodology is discussed.

The variety of optical components produced using this ion- assisted-deposition (IAD) technique, spans a wide ken of applications: immersed beamsplitters; band pass and edge filters; laser filters; IR windows; durable anti-reflection filters, fiber optics, and enhanced metals. Each product type has a specific set of constraints that establishes the design and production strategy: substrate type, material indices, intrinsic stress, temperature, distribution, uniformity, thickness monitoring, spectral performance specification, and environmental requirements. The end-Hall IAD processes were performed using an ion-beam current of approximately one Ampere over a range of 40 to 120eV, providing a uniform ion current density impinging on a large substrate area. Compared to films deposited using either conventional physical vapor deposition, or standard gridded ion sources, this process produces optically stable films with abroad ion-beam that is well suited for volume manufacturing of complex optical coatings.

Some of the commercial available ion based technologies like APS (Leybold AG), Mark II (CSC), Ion-Plating (Balzers) and NTQ (Carl Zeiss) have been compared and investigated for supporting our coating production lines. A comparative study has been worked out including the ability of upgrading conventional plants, resulting production costs, batch time, temperature load and scatter and mechanical durability of the coatings.

Plasma ion assisted deposition was used to deposit SiO₂ coatings on polycarbonate and on silicon. To study the influence of ion bombardment during the deposition process the bias voltage as an equivalent for ion energy was varied. At a definite bias value surface microtopography is changed abruptly. Coatings deposited at higher bias voltages show a stable chemical composition and therefore constant optical properties can be expected. It was also found that the barrier effect of coatings against moisture uptake, measured for polycarbonate substrates, increases with bias voltage.

With a modified standard coating plant simultaneous evaporation was applied to produce IR-coatings with improved performance for different applications. In one case, a single layer coating, quasi-homogeneously mixed from two different materials, achieves lower reflectance and higher laser damage thresholds at 2.78 micrometers. In another case, for a multilayer coating, 'soft' transitions between the individual layers yield a layer stack with a completely different structure with different properties, e.g. showing significantly reduced scatter.

Optical systems used in space and military applications require proof of performance of components at acceptance of contract and an active QA system in use throughout manufacture. To underpin these and other requirements the National Physical Laboratory (NPL) provides reference standards of regular reflectance that are individually calibrated to a known uncertainty of absolute measurement under conditions that match the customer's needs. These standards are necessary because of the significant errors that often occur when reflectance accessories are installed in IR spectrophotometers. The nature and causes of the errors are discussed, and why they are worse in IR instruments than in UV/visible ones. The NPL techniques, equipment and special modifications are described. Measurements can be made for angles of incidence up to 80 degrees, but for angles above 15 degrees it is essential to use polarizers, and NPL uses these in mutually reinforcing pairs at accurately set azimuth angles to achieve an adequate degree of polarization. The transfer standards supplied consist of overcoated or non-overcoated aluminized mirrors, or of uncoated glass to give a range of low reflectances. Stable coatings submitted by customers are also standardized, and in some case these have the advantage of giving an advantageous like-with-like measuring situation for the customer.

Substrate properties, coating design, and deposition process determine the surface morphology of optical coatings. The contribution of each factor can be estimated by measuring the surface topography with a scanning force microscope (SFM) and calculating the power spectral density functions. We present results for oxide and fluoride coatings on well polished glass and silicon substrates. The scattering of the coatings is predicted by calculations based on SFM data and compared with results from angle resolved scattering measurements.

The French Megajoule Project requires polarizers with high laser-induced damage thresholds. Such polarizers must be deposited on silica substrates, which are commonly prone to stress leading to early failure. Better stress control in the films require an optimization of the stack design as well as the deposition parameters. The thermal e-beam technique is used. We present the spectral behavior of such 1.03 micrometers polarizers in air and under vacuum at the Brewster incidence angle of 55 degrees 4 along with the damage test results.

In many applications in the field of optical coatings low dimensions and low weight of the substrates are of increasing importance. Organic substrate materials or thin glass substrates are used in many cases. Due to the low mechanical stability, these substrates are very sensitive against bending caused by the stress of the coatings. The stress of optical coatings deposited with plasma-IAD with the APS (advanced plasma source) was investigated. Based on the bending radius of coated thin glass substrates stress values were evaluated. It was found, that film stress can be influenced significantly with the deposition parameters and the use of the coating starting materials. The results of single layer coatings of various dielectric materials and completed multilayer systems are given.

A novel device, the fast-scanning acousto-optic spectrophotometer, was used to measure the in situ reflectance of a thin film during deposition. The reflectance data, which was measured at different film thicknesses and over a wavelength region from 400 to 1100 nm, was used to study the refractive index profile of inhomogeneous ZrO₂ films. This data was subsequently analyzed using a homogeneous thin film model to derive an 'effective' refractive index profile.

The optical systems surfaces share some features such as lateral uniformity, smoothness and well determined layers suitable for using of Rutherford backscattering method (RBS). RBS is nondestructive and its principle is very simple: the energy of scattered particles from originally monoenergetic beam depends on target atoms mass and their position under the surface. A modern PC procedure for RBS data evaluation GISA3.99 has been used accounting many theoretical details. The evaluated parameters are composition stoichiometry, layers thickness, impurity contents and/or depth profiles. Examples of measured systems are those with varying refractive index, modified surfaces, implanted systems, photoinduced Ag diffusion, ferroelectric ceramics, magneto-optic recording media, hard and protection coatings, luminescent silicium, laser mirrors systems and medieval glass weathering. An example of evaluation procedure of unknown six layer system is shown. The investigated systems are prepared by various methods: conventional and reactive evaporation, rf and dc magnetron sputtering, laser ablation, ion beam assisted deposition, plasma jet and sol-gel technique. There are some limitations of RBS method with surface roughness and with precise knowledge of cross-section and stopping powers. In spectra of complex structures, there may also be interference of signals from various elements and from various layers. Nevertheless, the RBS technique has a number of unique features and it is in many cases irreplaceable.

Micropatterned interference filters have been developed by dry etching of dielectric multilayer stacks. Apart from the optical demands on the conventional filter design there are new requirements originating from the patterning process, which has to be stopped at the interface between two layers. In this paper the fundamental problems associated with the design and the development of micropatterned multilayer dielectric stacks are discussed. Details of the production of a two-stage filter array are described and experimental results are presented.

Thin-film plate polarizers with a polarization ratio T_p/T_s > 1000 for single laser wavelengths can be realized if a Fabry-Perot filter is used. The spectral width of the polarization region of the filter polarizer is smaller than that of the usual long-wave pass filter, but there are not the practical difficulties of depositing multilayer systems with a large number of layers having nonquarter-wave thickness. For theoretical analysis, the principle of equivalent layer is extended to the Fabry-Perot design. Experimental results of the Fabry-Perot filter polarizer for different laser wavelengths, and with different coating materials, are presented.

Monitoring of stratospherical ozone depletion by filter radiometers calls for narrowband filters with outstanding parameters. At filter wavelengths down to 300 nm narrow bandwidth, high peak transmittance together with high out- of-band blocking especially at longer wavelength are demanded. Furthermore, filters have to be completely free of wavelength shift caused by humidity. Conventional interference filters suffer from such shift because of the water sorption of the evaporated layers. By using plasma ion assisted deposition of zirconia and silica layers we succeeded in manufacturing blocked two-cavity filters with full width at half maximum of 1.7 nm and peak transmittance of 17 percent to NIR optical density is at least 6. There was no decrease in wavelength of such filters by changing relative humidity from 100 percent to 0 percent. Corresponding conventional filters shifted 4.5 nm under the same conditions. The filter performance achieved allows use for the development of sensitive and specific instrumentation for environmental, climate, and meteorological research.

High quality coatings of aluminium oxynitrides have been deposited by reactive RF sputtering of aluminium in argon/oxygen/nitrogen atmospheres. Graded-index films in which the refractive index changes continuously with thickness over the range 1.6-2.0 have been produced by varying the oxygen and nitrogen content of the growing film. Computer control of the gas flow rates has allowed the reproducible production of laser rejection filters having optical densities greater than 4 and rejection wavelengths which can be chosen from < 300 to > 1100 nm. Scanning electron microscopy has shown that films when broken, tend to fracture preferentially at one particular composition. Depth profiling chemical analysis of the films has been carried our using x-ray photoelectron spectroscopy, showing clearly that the desired sinusoidal composition variations with depth has been achieved in these films.

The performance of UV photolithography lens-systems with usually several ten optical components is limited by both the quality of the substrates and by the quality of the optical coatings. The key problems are the quality of the reflectance over large and strongly curved surfaces, the absorption and scatter losses and the behavior during heavy UV irradiation in production lines.

A comparative study of yttrium fluoride thin films deposited either by conventional e-beam evaporation or ion beam sputtering (IBS) processes was made. Each coating was systematically characterized in terms of chemical composition, density and optical properties in the near UV- visible and IR wavelength ranges. The evaporated films exhibited low densities whereas the IBS coatings were found to be rather dense. As a result, the IR optical properties of the IBS films were more stable without any large losses related to water peak absorption at (lambda) equals 2.9 and 6.1 micrometers. Moreover, the reactive deposition conditions drastically decreased the IR losses of sputtered films in the 10 to 12.5 micrometers wavelength range. The films analyzed by Rutherford backscattering spectroscopy and nuclear reaction analysis were found refractive indices and extinction coefficients were precisely measured using spectrophotometric and ellipsometric methods as well as a photothermal deflection technique. The strong variations of the optical properties from one sample to another were thus correlated to the evolution of the chemical properties of the films. Finally, this work shows that IBS processes used in appropriate operating conditions can lead to low absorbing YF₃ thin films usable for applications that require transparency over a very wide wavelength range, from 0.3 to 12.5 micrometers.

The dependence of the silicon oxynitride (SiO_xN_y) refractive index on chemical composition can be employed in producing graded refractive index optical coatings. In this work, SiO_xN_y thin films were deposited by dual ion beam sputtering. Samples with different composition were obtained by making use of SiO₂ and Si targets. The energy and the ion to atom arrival ratio were also varied to study the correlation with the film stoichiometry. Infrared spectroscopy of the vibrational modes was used to investigate the composition of the samples. X-ray photoelectron spectroscopy and x-ray induced auger electron spectroscopy were combined to provide further insight into the chemical composition of the films.

Silicon oxynitride thin films were deposited on various substrates by dual ion beam sputtering from a silicon target in an argon oxygen nitrogen mixture. The composition and density of the films were deduced from Rutherford backscattering spectroscopy and nuclear reaction analyses. The residual stress was determined by measurements of the radius of curvature of the silicon substrates. The refractive index, extinction coefficient, composition and residual stress were investigated as a function of oxygen flow rate and deposition rate. The composition of the deposited materials was found to vary from Si₃N₄ to SiO₂ with increasing oxygen flow rate. The resulting films were dense, stable and insensitive to ambient moisture. A strong correlation between the compressive residual stress and the nitrogen content of the films was established. The origin of residual stress and its evolution with deposition parameters and composition of the films are discussed.

Titanium oxynitride (TiO_xN_y) thin films are of great interest for the fabrication of protective optical coatings. By varying the oxygen and nitrogen content in the films, the electrical, optical and mechanical properties of these coatings can be tailored properly. In this work, we fabricated TiN and TiO_xN_y films by dual ion beam sputtering technique. TiO_xN_y films were ion-assisted by a low energy oxygen and nitrogen mixed ion beam of variable O/N flux ratio. We observe that the incorporation of oxygen greatly improves the adhesion of the film on the glass substrate. Further, the optical extinction coefficient drastically decreases for increasing oxygen content, suggesting new applications of TiO_xN_y films as protective coatings on transparent substrates. The film composition by XPS analyses is in agreement with the results obtained by a simple model to describe the ion assistance phenomena. The crystallographic structure of the deposited films was characterized by using (Theta) - 2(Theta) x-ray diffraction and grazing incidence x-ray diffraction measurements. In the range up to 14 percent of the oxygen to nitrogen flux ratio, a TiN f.c.c. phase structure with preferred (111) growth-orientation of the grains is observed. For higher oxygen concentrations the absence of diffraction peaks suggests a more amorphous-like structure of the deposited film. Specular x-ray reflectivity measurements provide important and accurate information about the film-air and film-substrate interface roughness. The Kiessig fringes are caused by multiple internal interference of the x-ray beam and can be observed up to 3 degrees, which is a clear indication of the high homogeneity of the film thickness and of sharp interfaces.

Analysis of refractive index profiles of rugate and quasi- rugate films from measurements requires special techniques to avoid destabilization of solution due to a large number of fitted parameters. Regularization technique suggested recently takes into account a priori information about the index profile by adding the so called stabilizing operator to the merit function. We propose a more general form of this operator and different model of the system thus allowing for better correspondence between the stabilizer and a priori information. The new technique is demonstrated on the analysis of rf magnetron sputtered quasi-rugate films of SiO₂/TiO₂ with nominally linear material composition profiles and the results are compared to profiles established from Rutherford backscattering spectroscopy measurements.

The kinetics of photo-induced solid state chemical reaction of silver with a As₃₃S₆₇ films in conventional sandwich structure was measured by monitoring the change in thickness of the undoped chalcogenide using a modified computer-controlled technique. The kinetic data obtained shows that there are two stages in the photo-induced reaction process. Rate coefficient and activation energies have been measured and a comparison of the composition and structure of reaction products detected by Rutherford backscattering spectroscopy (RBS) has been made. The RBS spectra obtained at different stages of the photo-induced reaction process show a step-like form of the Ag concentration profile during the course of the reaction and the homogeneous distribution of Ag in the final reaction products, e.g. 31 at percent Ag. The step-like form of the Ag concentration profile is discussed in the framework of the G-c_Ag diagram for the Ag-As₃₃S₆₇ system. On the basis of the RBS results, it is suggested model explaining the kinetics of the photo-induced reaction.

The article presents the thin-film stack systems creating the new type of optical elements. The said element substitutes a thin-film plane polarizer and narrow-band interference filter simultaneously for selected wavelength. The comparative analysis of the new construction basic parameters was carried out in the function of beam incidence angle on the system with changes of analogical values for classical narrow-band filter. The narrow-band polarization interference filters for (lambda) equals 1064 nm have been designed and made with application of classical vacuum plant with electron guns.

The paper describes the design and realization of a dichroic mirror for a diode pumped YAG:Nd laser. The mirror is deposed on an optical glass substrate and works in optical contact with the laser crystal. The design was performed by admittance matching of the basic stack with the adjacent media. Proper matching stacks were selected between all possible solutions computed by analytical inversion of the system equation for the equivalent layer. Deposition conditions and experimental results are given.

A new Fabry-Perot filter based on a silicon wafer spacer is proposed in this work. IR gas sensors based on these filters would combine excellent selectivity and signal-to-noise ratio with an overall scheme similar to that of the simplest non-dispersive IR sensors. The filter can be fitted to the fine structure of different gases, in particular those diatomic with unlike atoms as carbon monoxide among others. The spacer of the filter is a silicon wafer of defined thickness. Fine tuning to gas absorption peaks can be reached by coupling it to other multilayers. In this work the properties of silicon wafers as spacers of the proposed filters are studied. From the study it derives that the most determining factor of the filter properties is the loss of coherence caused by surface roughness. However, as we demonstrate in this work, surface roughness limitations are not very severe and easily obtained by standard polishing procedures.

Plasma enhanced chemical vapor deposition is a novel process to produce metal-filled polymer films. Both bis-allyl-Pd-Cl and allyl-Pd-pentacyclodienyl precursors were used. In conditions dependent on precursor, pressure, electrical power, voltage, frequency and substrate temperature films of different chemical structure and morphology were obtained. Transparent films and absorptive amorphous ones were deposited. Film structure could be both mixture of particles and Pd particles surrounded by organic matrix. The complicated structure of organic part of Pd-based films can be explained by some chemical syntheses taking place during plasma process. The film sensitivity to laser irradiation and writing threshold dependent not only on Pd content but also on phases distribution morphology. Film sensitivity correlates with its electrical resistivity. Thermal stability correlates with cross-links quantity. Pd particles were not oxidized under 450 degrees C annealing.

Subwavelength structured (SWS) surfaces etched directly into different substrates provide performance equivalent to an ideal anti-reflection thin film. We report on SWS surfaces etched into silicon which present anti-reflection properties for visible light. The fabrication of the SWS component is based on a double holographic exposure of photoresist and reactive ion etching processes. At normal incidence, the reflectivity for the HeNe line is 0.02. This reflectivity measurement includes a 1 percent diffusion by the surface. Measurements of the reflectivity over the whole visible spectrum and over a wide field of view are provided.

The structure evolution characteristics of MgF₂ and NdF₃ optical thin films on CaF₂ (111) substrates have been investigated by cross sectional transmission electron microscopy and atomic force microscopy and were related to their extinction coefficient. The films were deposited by physical vapor deposition under ultra high vacuum conditions. A series of experiments have been carried out at various substrate temperatures at 300 nm thickness and by the stratification of the two fluoride materials. The structure evolution of single and stratified films was investigated and discussed in relation to the structure zone models. The effect of stratification on the structure and extinction coefficients is discussed in comparison to the effect of segregating impurities. The development of morphology of stratified films is analyzed in relation to the thickness of the interlayers and temperature. The optimum conditions for preparing films of low extinction coefficients are found at parameters corresponding both to the transition between zone T and zone II growth and to the formation of nanocrystalline structures.

Pilkington Optronics (Barr and Stroud Ltd) has an ongoing development and pre-production activity for ultra-durable coatings. Such coatings provide enhancement of environmental durability of IR transmissive windows and domes on airborne platforms. This activity places particular emphasis on providing protection against rain and solid particle impact at airborne velocities. This program has produced a very effective rain and san d erosion protective, anti-reflective multilayer, based on boron phosphide overcoated with diamond like carbon (DLC/BP). This coating has been demonstrated on a range of IR materials: germanium, FLIR ZnS, TUFTRAN, silicon and gallium arsenide. This paper describes a pre- production program to coat the external, face of the AV-8B and GR-7 navigational FLIR germanium windows. Results are presented of optical and environmental performance. Moreover, results of extended flight trials are presented which utilize optical scatter, transmission reduction and coating obscuration to compare durability performance of DLC/BP as compared with DLC. These tests show a factor of at least ten increase in window lifetime through use of boron phosphide.

The calculated performance is presented for a number of beamsplitters for the 10-200 micrometer spectral region. Designs based on pellicles as well as solid substrates are presented. Average efficiencies that are greater than 0.9 appear possible for this range of wavelengths. The implementation of the above designs will present considerable challenges. Difficulties that will have to be overcome in the manufacturing process are enumerated.

The computer-controlled electron cyclotron resonance plasma enhanced chemical vapor deposition of SiO_xN_y was used for the manufacturing of optical interference coatings with inhomogeneous and traditional multilayer refractive index profiles. Such complex structures as triple-band rugate optical interference filters and graded refractive index antireflection coatings were grown. The design of coatings was performed using measured optical constants of the SiO_xN_y-system.

Storage ring FELs (SRFELs) recently demonstrated to be useful coherent light sources for applications in several branches of scientific research. In particular, the super ACO SRFEL provided UV light at 350 nm for successful operations in a time resolved fluorescence experiment on a biological molecule and in the first two color experiment combining synchrotron radiation and FEL light. Up to now, SRFELs are characterized by a relatively low gain and hence, great care must be invested on the choice of optical cavity mirrors. In this paper we relate the several characterizations performed on different set of mirrors and the obtained results.