Advanced deposition technologies produce optical coatings with state-of- art-optical performance, improved durability, stability and lifetime and sometimes improved scalability to large optics and small-optics volume coating. This paper examines a low-energy, high-flux reactive ion assist process developed at Itek during the past four years from this perspective. The process is introduced at the fundamental level of ion and atom energetics and arrival ratios, with both inert and reactive gases. Earlier high-voltage, low-current approaches are contrasted. The manifold benefits of coating densification, improved stoichiometry, low-temperature processing and in situ substrate cleaning are described. Process implementation in mid-sized and large coating chambers is pictorially illustrated. Inexpensive retrofit is realized. Very low absorption, enhanced durability and precision mechanical stress control are demonstrated with selected highlights of recent Itek optical coating experiences. Examples of especially-interesting optics recently coated are shown. Competing coating technologies are compared.

Silicon dioxide has many desirable properties as a coating material for the visible and near IR spectrum. These include low index, high transmittance, good adhesion, and environmental durability. The deposition of the material from solid discs or granular forms using an electron beam gun tends to have a fluctuating angular distribution. This causes reproducibility problems in some critical optical coating processes. Silicon monoxide can be evaporated from a resistance source with a highly reproducible deposition pattern, but it does not have the low index and high transmittance required. We report on attempts to develop processes which convert the SiO to SiO₂ during deposition by the use of ion assisted deposition. The additional oxygen must be supplied in a sufficiently energetic process to provide the material conversion during or after the SiO deposition on the surface to be coated. The deposition rate (10 angstrom per second), the uniformity, and the repeatability of the processes must also be adequate for the production of the product at an economical rate. These experiments have been done with both an End-Hall and a Cold Cathode ion source. A comparison of the results and behavior observed with each type of ion source are reported along with recommended process parameters to be used with each.

The development of advanced deposition technologies is continuously evolving for the synthesis of oxide coatings used in optical applications. Recent progress is made in the use of magnetron sputtering to reactively deposit metal-oxide thin films. The sputter deposition parameters are chosen with respect to the reaction kinetics of the metal-oxide system to enable a variation of composition along the film growth direction. The key process parameter to control is the sputtering rate of the target. The shape of the composition profile directly corresponds to the preselected variation of deposition rate. By simply varying the sputtering rate using a working gas that consists of an inert-oxygen mixture, structures are synthesized with composition profiles which can be either abrupt or graded in the growth direction. The result is a compositionally modulated structure of the metal-oxide system. This procedure for composition modulated synthesis is demonstrated for metals which are highly reactive with oxygen as well as for those metals which are not. The development of this deposition methodology will facilitate the design of metal oxide films for optical applications, as in gradient-index filters for example. Results are presented for the reactive sputter deposition of metal oxide coatings in the yttrium-oxide, molybdenum-oxide, and copper-oxide systems.

Plasma-enhanced chemical vapor deposition (PECVD) offers an alternate route to optical thin films, but the relative merits vs conventional methods and between different excitation processes must be evaluated. We investigated the microwave and rf PECVD of SiO_x and SiO_xN_y films using tetraethylorthosilicate (TEOS) mixed with nitrogen, oxygen or nitrous oxide. Plasma emission spectroscopy revealed variations in reactive species' concentrations for different process conditions. Deposition rates were traced for two series of microwave PECVD reactions, and are compared to other processes. For both rf and microwave PECVD processes, film stoichiometry was characterized by IR and Auger spectroscopy. Optical properties were assessed by ellipsometry, IR and visible spectroscopy. Both microwave and rf PECVD process conditions were identified that form SiO_x with less than 2% residual carbon. By varying process conditions, one can span a broad range of SiO_xN_y formulations. Variations in optical properties and film microhardness with changing film stoichiometry are discussed.

A large format ultra-narrow bandpass filter for use in the visible through near IR which has improved transmission and environmental stability is discussed. The filter is composed of thin films of metal- oxide coating materials deposited at near bulk density using OCA's MicroPlasma coating process. The high packing factor of the coating results in nearly zero vacuum to air shift. The filter shows improved temperature stability due to the selection of coating materials with low coefficients of thermal expansion and temperature coefficients of refractive indices as compared to filters manufactured using conventional technologies. In addition, the materials also have very low optical absorption and scatter which leads to improved filter transmission. Experimental data is presented describing the spectral performance and humidity and temperature stability of multiple cavity filters with bandwidths of 10 angstroms or less which possess single piece (non-mosaic) clear apertures of up to 10 inches. The improved temperature stability can eliminate the need for active temperature controllers such as heating cells. Improved narrow band filters have several immediate applications as a method to improve signal-to-noise ratio of laser based optical systems for both military and commercial markets such as LIDAR, FTIR, and remote sensing.

Inertial Confinement Fusion (ICF) research has historically been a driver in the development of high performance, high damage threshold optical coatings. This is particularly the case now as the ICF community develops plans for a proposed 1.8 mega-joule solid state (Nd⁺³-phosphate glass) laser system. The new system, the National Ignition Facility, is possible in part due to advances in optical coatings technology including the laser-conditioning of multilayer dielectrics and broadened applications for room-temperature deposited coatings. Sol-gel AR coatings are the standard for large, high-power laser optics and sol-gel HR coatings are being developed. For mirror and polarizer coatings, e-beam-deposited dielectrics continue to provide the highest damage threshold coatings, but their laser damage thresholds and optical performance are limited by micrometers -scale defects and poor control over layer thickness, respectively. More energetic deposition techniques such as IAD and IBS, now popular in the commercial market, offer both advantages and disadvantages in this high-damage- threshold coatings market.

A correlation between laser-induced damage and the height of a coating defect was found from an examination of HfO₂/SiO₂ mirrors made by three different coating vendors. The nodular defects in these reactive e-beam deposited mirrors were studied using the combination of scanning electron microscopy (SEM), optical microscopy, focused ion beam (FIB) and atomic force microscopy (AFM) techniques. Each vendor has small defects in common, but characteristically different large defects. also the majority of seeds that caused the defects were made of hafnia, not silica. The apparent mechanical stability of the defects within the coating plays a major role in the laser resistance (1064 nm and 10 ns) of a high damage threshold coating.

An attempt is presented of a systematic experimental approach to the problem of scattering and roughness modification after deposition of an optical thin film. BK 7 substrates with different surface qualities have been coated with evaporated MgF₂, LaF₃ and magnetron sputtered SiO₂ and Nb₂O₅ films as representatives of low index/high index columnar structured and structureless films, respectively. Investigations by total integrated scattering (TIS) and angle resolved scattering (ARS) at 633 nm and 325 nm as well as atomic forced microscopy (AFM) demonstrate the possibility of quite different effects of scattering and roughness modification to occur.

Pure aluminum films have the highest reflectance among all metals in the far-ultraviolet (FUV) wavelength range extending from 120-230 nm. Unfortunately, aluminum is a highly reactive material and is only free of oxidation when deposited in an ultra-high vacuum chamber (p < 10^-10 torr). Aluminum films prepared in high-vacuum (conventional) chambers (p approximately equals 10^-6 torr) always oxidize regardless of deposition technique, deposition rate, and substrate temperature. Therefore, if a conventional chamber is sued for fabrication of aluminum multilayer devices based on theoretical designs, each aluminum film in the theoretical model should be considered as at least a two-layer structure of aluminum and aluminum oxide film.s Spectral performance optimization of an aluminum mirror is possible if the thickness and optical constant of the oxidized part of the aluminum film are known. Experimental results where XPS depth profiling was used to determine oxide thicknesses are reported.

Thin films of gold and platinum have been deposited onto super-polished fused silica substrates using thermal evaporation, ion assisted deposition (IAD), sputtering and ion assisted sputtering. The influence of ion beam flux, coating material and deposition rate on the films microroughness have been investigated. Coatings of gold and platinum have been bombarded with low energy (10-20 eV) Ar ions from an electron cyclotron resonance (ECR) ion source during deposition. Short range surface microroughness of coated surfaces has been examined using scanning tunneling microscopy (STM) and atomic force microscopy (AFM), while long range surface microroughness has been characterized using an angle resolved optical scatterometer. Results indicate that bombardment with low energy ions cause significant reduction in microroughness of metal coatings.

Thin films of titanium, zirconium, and hafnium nitride are prepared by DC magnetron reactive sputtering at room temperature on fused silica, optical glass and silicon substrates. Deposition parameters are investigated in order to obtain stoichiometric films. The optical and electrical properties of the films as a function of nitrogen partial pressure are determined. The results show that an inverse correlation exists between the optical reflectance and the electrical resistivity of the films. The optical constants of the films are determined by Variable Angle Spectroscopic Ellipsometry (VASE) measurements from 240- 1700 nm at 10 nm steps. Deposited film composition is obtained by the Rutherford Ion Back Scattering (RBS) method. The rms roughness of the films is measured by using an optical scatterometer. Ellipsometer data for all three films show that their refractive index (n) in the visible spectrum is decreased by increasing the film thickness while the extinction coefficient (k) is unchanged. Thin films of TiN have the lowest room temperature resistivity (approximately equals 75 (mu) (Omega) - cm) relative to ZrN and HfN thin films.

An optically variable film (OVF) is designed to exhibit a significant color shift with changing observation angle. This color shift was characterized by multi-angle reflectance measurements using a goniospectrophotometer system that also calculated the angle dependent performance of the optically variable film. The reflectance and color of the optically variable film were predicted by optical thin film modelling and compared to the measured values. The optical constants of the materials used in the OVF were then modified based on the goniospectrophotometer measurements to estimate the reflectance more accurately and thus improve the modeled color predictions. Automating this iterative procedure to assess the refractive indices of the OVF components using multi-angle reflectance measurements could create an additional tool for monitoring the fabrication process.

A thin layer of homogeneously oriented nematic liquid crystal (NLC) applied on the optical-quality surface as a free film may visualize, through a polarizing microscope, the images of defects that can not be observed with conventional microscopy: cleaning defects, local physical and chemical surface modifications and microrelief defects. A new vision of polished glass surface defects obtained by the NLC thin-film coating makes it valuable as independent technique for surface quality testing.

A Mueller matrix imaging polarimeter has been developed and demonstrated for characterizing the polarization properties of optical coatings in place in optical systems. This Mueller matrix imaging polarimeter is a form of ellipsometer which measures the polarization characteristics of ray paths through systems in image form. It is a highly versatile instrument capable of making a variety of polarimetric measurements on optical samples or entire optical systems. Two data sets will be presented. The first shows the polarization behavior for example lenses which display the typical Maltese cross variation. The second shows images of polarizing beam splitter behavior as a function of angle of incidence, clearly showing how the plane of polarization as determined by the s- and p-planes rotates for light incident out of the normal plane.

Diagnostic coatings have been designed with predicted absorptances twenty to forty times that of quarter wave stack high reflectance laser coatings even though the film layers have the same very low absorption indices. The diagnostic coatings can precisely reveal the values of the absorption indices of individual thin film materials with metrology of modest accuracy. These designs may enable coating producers to evaluate alternate film materials and changes in deposition processes accurately and rapidly. One diagnostic design distinguishes between bulk film absorption and layer interface absorption. Improved film material properties data will result in better predictions of the performance of new designs and may result in the development of new designs with reduced sensitivity to bulk film or interface absorption. Matrix equations are used to relate coating absorption to film absorption indices for normal incidence quarter wave stack coatings.

A flexible numerical procedure for the calculation of thin film optical constants from specular transmittance and reflectance data is presented. The method is based on the minimization of an error function, which may be adapted to the specifics of the optical behavior of the given sample (or set of samples), and the given wavenumber region. The flexibility in choosing an appropriate form of the error function minimized, in combination with the powerful minimization method of conjugated gradients, allowed us to investigate the optical constants of very different types of novel thin film materials with a complicated absorption behavior. In particular, the results concerning the investigation of single- and two-layer-systems based on the following optical thin film materials are presented: amorphous silicon, phthalocyanine layers, hydrogenated amorphous carbon, and as-deposited (rough) CVD diamond layers.

The validity of the Fourier transform theory is investigated in the context of bandpass filters.

The design of polarization insensitive optical coatings via use of the needle synthesis algorithm in combination with second order optimization methods is explored. Several designs produced with this technique are presented and comparisons are made with the results of other design techniques drawn from the literature.

A mathematical model was constructed in order to evaluate line of sight thin film deposition geometries for uncooled annular resonator optics that have very low absorption high reflectance coatings. Model inputs include thin film source distribution profiles, source offset location and orientation, substrate surface profile and dimensions, substrate height and rotation, and radially varying masks if required. The model calculates the uniformity of the resulting films as well as other parameters that affect film quality such as deposition angles and relative deposition rates. This paper presents the results of the analysis for the Alpha laser beam compactor and rear cone. The use of tilted deposition sources promises to improve film quality, uniformity, and producibility. The model is readily revised to include additional constraints of concern to vendors and end-users. A mask concept is proposed to minimize film quality degradation due to intermittency effects.

The temperature of an object in space in influenced by many factors, including the optical properties of the surfaces exposed to the environment. These properties can be modified by applying coatings. This paper describes a case study of such an application of thermal/optical properties control and the effects on the system that result. The example cited is the solar power panels used for satellites. The prime need for a space power system is maximum output per unit of mass. If the temperature of the array can be lowered the output will rise. Coatings on the front surface of a panel can reduce the temperature by modifying the solar absorptance and the emittance. Some coatings reflect the unwanted energy from the surface without changing the amount of usable energy that gets into the cell. Other coatings increase the ability of the panel to radiate heat and thereby remain cool. Specific examples of coatings for use on silicon (Si) and gallium arsenide (GaAs) cells will be discussed, and the quantitative gains that can be obtained will be estimated based on a thermal model of an array. The temperature reductions for such cells for various types of coating treatments (reflecting the sun in the UV, reflecting the near infrared, or increasing the far infrared emittance) and the expected increase in output form an array will be covered in these discussions. In an application where a 1% to 2% increase in output may be highly desirable, this discussion will show how 3% to 5% increases in output may be obtained.

Large-optics coating facilities and processes at Pacific Northwest Laboratory (PNL) that were used to develop large-area high-performance laser mirrors for SDIO are now being used to fabricate a variety of optical components for commercial clients, and for novel applications for other DoD clients. Emphasis of this work is on technology transfer of low-cost coating processes and equipment to private clients. Much of the technology transfer is being accomplished through the CRADA (Cooperative Research and Development Agreement) process funded by the Department of Energy (DOE).

Genetic algorithms, developed by J. H. Holland, are randomized search algorithms which mimic the mechanics of natural selection and natural genetics. In this work a genetic algorithm was applied to optimization of sophisticated thin-film systems. It was found to be an efficient tool rapidly converging to the target as defined by the merit function. The algorithm is introduced, discussed, and illustrated for two applications: a polarization-preserving coating of a penta-roof prism for a long-grange optical sight and a phase light splitter--beam divider/combiner for bi-directional fringe-counting interferometers.

The twisted nematic liquid crystal display (TN-LCD) is the leading technology for high performance flat panel displays. However, the region of high contrast for TN-LCD's is limited. Birefringent elements, of compensators, may be used to provide improved contrast at high viewing angles. The phenomenon of form birefringence has been used to design a compensator that can be fabricated by physical vapor deposition of silica and titania, two common coating materials. Improved viewing angle characteristics, particularly in the horizontal direction, have been demonstrated using the compensator. The 20:1 isocontrast region has been extended to +/- 50 degree(s) in displays incorporating the compensator, an improvement of 10 degree(s) or more relative to uncompensated displays. The compensator design includes integrated antireflection coatings to reduce glare. In this way, display legibility is maximized in the presence of both high and low ambient illumination.

The need for transparent conductive coatings on plastic aircraft transparencies has produced significant improvements in low temperature indium tin oxide (ITO) coating technology as well as the control of sputter deposition uniformity across complex shapes. ITO coatings with bulk resistivity of 6.2 X 10^-4 ohm-cm, carrier concentration of 3.6 X 10²⁰ cm^-3 and mobility of 28 cm² V^-1s^-1 have been routinely produced on unheated polymer substrates. Transmission through the visible and near infrared can be tailored to each application by adjusting sputtering process parameters. While tuning transmission, care must be taken to maintain low resistivity by balancing carrier concentration and mobility. Techniques for coating thickness control by the relative motion of transparency and sputtering targets are discussed. The large scale production of low resistivity ITO coatings on temperature sensitive substrates will require careful attention to process control.

Multilayered coatings were made by physical vapor deposition (PVD) of a perfluorinated amorphous polymer, Teflon AF2400, together with other optical materials. A high reflector at 1064 nm was made with ZnS and AF2400. An all-organic 1064-nm reflector was made from AF2400 and polyethylene. Oxide (HfO₂, SiO₂) compatibility was also tested. Each multilayer system adhered to itself. The multilayers were influenced by coating stress and unintentional temperature rises during PVD deposition.

Recent technology advances in the processing of polymeric multilayers has made possible the production of an all polymeric cold mirror reflector via coextrusion processing. The simultaneous formation of up to 5200 alternating layers of optically dissimilar polymers allows the continuous extrusion of a self supporting cold mirror at high linear speeds and widths of over 0.6 m (2 ft). The material can be post formed into shallow 3-dimensional reflector shapes, given proper attention to the initial film optical properties, the final part geometry, and forming considerations. The self supporting nature of the film allows it to be wound on rolls and stored for later part fabrication. Reflectance of 95-99% over the visible wavelengths has been achieved with commercially available polymers. The polymers used have high transmission in the near infrared region of 700-2000 nm, and sharp cut- on and cut-offs have been achieved. Uniformity of optical properties across the surface of the film will be discussed, as will thickness, angle of incidence, and temperature effects. The large area capability of this material may make possible applications for heat/light separation not previously viable due to deposition chamber size limitations or the high cost per area of conventional deposition technologies. Scale up of the process to much larger widths is feasible and will be discussed. Prototyped parts and potential applications of this new material will also be covered.

Weatherable, low cost, front surface, solar reflectors on flexible substrates would be highly desirable for lamination to solar concentrator panels. The method to be described in this paper may permit such reflector material to be fabricated for less the 50$CNT per square foot. Vacuum deposited Polymer/Silver/Polymer reflectors and Fabry-Perot interference filters were fabricated in a vacuum web coating operation on polyester substrates. Reflectivities were measured in the wavelength range from .4 micrometers to .8 micrometers . It is hoped that a low cost substrate can be used with the substrate laminated to the concentrator and the weatherable acrylic polymer coating facing the sun. This technique should be capable of deposition line speeds approaching 1500 linear feet/minute². Central to this technique is a new vacuum deposition process for the high rate deposition of polymer films. This polymer process involves the flash evaporation of an acrylic monomer onto a moving substrate. The monomer is subsequently cured by an electron beam or ultraviolet light. This high speed polymer film deposition process has been named the PML process- for Polymer Multi- Layer.

In this paper we describe the spectral characteristics of transmission and reflection holograms in dichromated gelatin (DCG), and their dependence on process parameters. The aim of our research efforts was, to manufacture holograms with low absorption and scattering and well defined optical properties, as central wavelength, bandwidth, and refractive index modulation. Losses due to absorption and scattering can be minimized by employing inorganic hardeners. By means of process control it is possible to manufacture reflection grating holograms with bandwidths between 11 nm and well above 360 nm. It was found that the hardening time, exposure energy, dehydration temperature and initial layer thickness affect the bandwidth and central wavelength of reflection holograms strongly. The shift of the Bragg-angle of holographic transmission gratings depends on the pH- value of the swelling bath and was found to be lowest at pH 9.

The usage of plastic substrates has known a big enhancement driven by ophthalmic applications, but a further spreading can be foreseen in higher technological fields too. As known, two drawbacks are outlined when using these substrate: low scratching resistance; high thermal expansion coefficient, thus bad compatibility with the optical coatings made of inorganic layers. The most widespread solution up to now is a hardening and mechanical matching lacquer coating by dipping, which is well accepted in ophthalmics, but cannot be utilized in precision optics due to its intrinsic thickness disuniformity. Recently similar layers have been realized by Plasma Enhanced Chemical Vapor Deposition. This paper describes Ce.Te.V.'s activities and results in setting up this coating by RF PE-CVD, aimed to both ophthalmics and precision optics. The two different functions (hardening and mechanical matching) and the performances of the coating-with special attention to scratch and thermal shock resistance-are examined. The experimental equipment and the optical and environmental characteristics are described.

The suitable layer-building solutions containing tin and phosphorus or tin and phosphorus plus fluorine compounds were prepared. Simple spray pyrolysis technique for obtaining thin SnO₂:P or SnO₂:P, F films on glass or quartz substrates is used. The effect of different parameters such as dopant concentration, substrate temperature and carrier gas flow-rate on film properties is presented. some physical, electrical and optical characteristics of the prepared thin SnO₂:P and SnO₂:P, F films is discussed.

Due to high launch vehicle costs, space instrumentation designers are constantly pressured to decrease weight and increase reliability of flight hardware. To meet these needs in a spectrometer, the infrared products team at Optical Coating Laboratory, Inc. (OCLI) and the NASA Goddard Space Flight Center (GSFC) have developed an infrared logarithmically variable filter for use in NASA's Pluto Fast Fly-by instrument. The filter and diode array combination replaces the multiple optical elements in conventional spectrometers, resulting in lower instrumentation weight and complexity with no moving parts. The choice of logarithmic rather than linear profile yields constant resolving power on every pixel of the array. Filters were produced in which the center wavelength varied from 1.0-1.581 micrometers , and 1.581-2.5 micrometers over a distance of 1.024 cm. Bandwidth was 0.3% FWHM and overall transmittance ranged from 30% to 50%. This paper discusses the major issues and tradeoffs in the design, manufacture, and testing of the filters. Measurement techniques are presented and comparisons are made between theoretical and measured performance of bandwidth, transmittance, and spectral profile.

The advantages of optical coatings realized by Sputtering versus thermal evaporation by crucible or Electron Gun, are very well known, but this technique is used only partially for dielectric coatings despite of a wide use in semiconductors and microcircuits, due to the slowness of RF Sputtering processes when starting from dielectric targets. This paper describes a DC Reactive Magnetron Sputtering technique from metal target set up at Ce.Te.V. for deposition of multilayer coatings, with cycle times comparable-or even faster-than conventional solution. The advantages of this process consist in obtaining films with high optical and mechanical performances with high repeatability on room temperature substrates. Pumping cycle can thus be faster and dead time for substrates heating and cooling down can be avoided, characteristics which plastic substrates can particularly take advantage of. Performances of the realized coatings on glass and plastic substrates, together with cycle time and material costs, are finally compared to results obtainable by Electron Beam Gun Reactive Deposition.