The needle optimization technique has been developed so as to agree a necessity of the mathematical formalization of the design problem with a specific uncertainty of the concept of the optimal design. It allows to find a practically optimal design in the course of the design process. Future developments of the needle optimization technique are connected with a search for multiple solutions to the design problem and with a search for optimal solutions when new non-standard formulation of the design problem are used.

There are many advanced local and global optimization techniques, such as Gradient, Simplex, Flip-flop, Needle, Genetic and Simulated Annealing, which have been successfully applied to optical thin-film design. However, all these optimization techniques either require a selection of a reasonable starting design, which is a big obstacle to an inexperienced designer, or they have some kind of inbuilt random feature, which may give rise to different answers each time. To find the true global optimized solution for a thin film design problem, we need to solve an array of interlinked multi-dimensional simultaneous equations. Until recently, for more than just a few layers, this has been a very difficult task, requiring the use of a supercomputer and highly skilled programming. By using orthogonal Latin Square theory and an experimental design methodology in a search space reduction process, a Windows based program has been written that can operate on even a 20 MHz 386 computer. It can find the global optimum design for up to 23 layers using as many dispersive and lossy materials as one wishes, within a period of hours. Additionally this methodology (called DGL-Optimization) allows the use of multiple target spectra with such as both s & p polarization, for reflection and transmission simultaneously.

We demonstrate that the needle optimization technique enables the effective design of optical coatings for applications which require a specific spectral response over a wide angular range. A preliminary choice of the most useful layer materials is discussed in connection with the question of the design optimality. It is shown that in many cases two-material designs with the lowest and highest accessible refractive index values are optimal from a practical point of view. It is also shown that in some cases intermediate refractive index values are quite necessary to achieve a good approximation of design targets.

The combination of discrete and Rugate filter design techniques can provide unique design advantages. Rugate filter deposition techniques can be applied to discrete, and square wave based designs as easily as they are applied to sine wave index profiles. Just as apodization reduces sidelobes about a Rugate stop-band, apodization reduces sidelobes of a square wave filter. This paper builds on these observations to present designs which superimpose sine and square wave profiles to produce a more efficient use of the design space. Techniques are presented for moving back and forth between discrete and Rugate designs to achieve reduced film thickness, more efficient use of index contrast, and harmonic suppression.

A new optical computation method for the monitoring of chemical reactions requires filters with spectral transmittance curves that vary in a complicated way with wavelength. In this paper we consider the design of two different sets of filters, one of which could be used to predict the degree of curing of a polymer from an analysis of its Raman spectra. The problem is not easy because the required filters have sharp spectral features in a narrow spectral region. Two different design methods are used. The performance of one set designed by conventional means is very close to the specifications. However, current thin film deposition methods are probably incapable of producing filters of such thickness. The second solution is based on the use of several filters placed in series. It should be possible to implement this particular solution, but its performance is not nearly as good. Nevertheless, calculations indicate that this filter pair should also result in a satisfactory control of the curing process.

A thin film synthesis technique based on the refinement of inhomogeneous systems is improved by the implementation of simultaneous refractive index and thickness optimization. Severe artifacts generated at oblique incidence by an earlier version of the method are eliminated. Complex designs comparable to published solutions synthesized with the Needle Method are demonstrated.

In the production of a multilayer metal-dielectric bandpass filter, there are advantages in a design that is asymmetrical. A silver-dielectric stack is used as an example. The induced transmission theory of Kard is used in the analysis.

The basic principles of guided mode resonance filters constituted by a high index modulated coating deposited on a classical glass substrate are presented. A rigorous method used to compute the reflection coefficients of this kind of structures is described. We show that in some cases, computation can be made by using an approximate method. These structures, which permit one to design narrowband inverse filters, are compared to solutions based on classical multidielectric coatings.

An inhomogeneous refractive index layer that follows a specific quintic (fifth-order polynomial) profile that smoothly matches the two-media interface is known to drastically reduce the nominal Fresnel reflection at this interface. There is so short wavelength cutoff for a quintic (or quintic-like) layer, as the reflectance continues to decrease with decreasing wavelength. Thus the quintic matching layer is a semi-infinite band antireflection coating. Furthermore, at the long wavelength end of the spectra the reflectance never rises above that of the Fresnel reflection at the bare interface, a feature not shared by multilayers optimized over specific bandwidths. A scaling relationship that relates the long wave cutoff of the total optical thickness of the quintic layer needed for a given reflectance level and for a given difference in media refractive index is described. For example, a quintic layer whose optical thickness is two waves or four halfwaves (at the longest wavelength of the band) will reflect at least four orders of magnitude less than the reflectance of the bare interface for all lower wavelengths. This paper also compares a quintic layer which is inhomogeneous to a needle-optimized multilayer design.

The guided mode and free space pattern of sources within multilayer planar micro-cavities is calculated. A single micro-cavity formula is emphasized that permits to have an energy balance controlled by the cavity poles. Numerical calculation is performed. The results allow to control spontaneous emission of overcoated micro-sources, as well as roughness-induced absorption of optical multilayers.

We investigate theoretically and experimentally the optical properties of planar Ta₂O₅/SiO₂ multilayer structures implanted with rare earth ions such as erbium and praseodymium. We demonstrate that the spontaneous emission can be strongly enhanced in a direction normal to the layers if the luminescent ions are located in the spacer of a resonant Fabry-Perot type microcavity. Nevertheless, we show that a large amount of light is emitted into the guided modes of the planar stack reducing the optical confinement which is likely to be reached within this type of dielectric microcavities.

The WKB (Wentzel-Kramers-Brillouin) method, well-known in quantum mechanics, is applied in the second-order approximation into non-uniform Bragg structure, such as rugged dielectric thin films, sinusoidal gratings, and holograms. In this paper, the analytic WKB problem solution will be presented including numerical results.

We investigated a new type of optical element: volume diffractive optical element (VDOE). The uniqueness of the VDOE approach lies in the fact that it can exhibit a high diffraction efficiency (indigenous to a volume holographic optical element (HOE), while sporting a multi-diffractive layer structure amenable to standard lithographic manufacturing techniques. Computer design flexibility and the capability of effecting an arbitrary phase function in a VDOE provide a number of potential applications for these optical elements. Specifically, space telescope and image multiplication are discussed. Our theoretical modeling of the VDOE utilizes the rigorous coupled wave theory, which allows us to introduce an arbitrary VDOE/spacer layer thicknesses, grating slant angles, wavelengths, and incident angles. In addition, our model can simulate a multi-layer phase shifted VDOE structure (important in simulating HOE structures by a multi-layer VDOE design).

We show how to use dielectric thin films in order to reduce scattering and maximize broad-band absorption in arbitrary rough overcoated black surfaces. A rigorous calculation is developed thanks to an improved differential method, and the results are compared to experiment. Scattering is reduced by a factor 10 (down to 5.10^-3), though the starting bare surface is a standard low-cost black paint (5.10^-2 scattering). Absorption can therefore be optimized up to 0.995.

The potential utilization of volume diffractive elements (VDOEs) in a variety of sophisticated imaging applications has been established. VDOEs are capable of designed-in arbitrary phase distributions (indigenous to multi-layer diffractive structures), while maintaining high diffraction efficiencies (exhibited in volume holographic optical elements (HOEs)). Furthermore, multi-layer VDOE structure facilitates further improvement over HOEs. High diffraction efficiencies with simultaneous side lobe suppression can be achieved in VDOEs, while narrow bandwidths and desirable free spectral ranges are maintained. In this paper, we show that with proper utilization of VDOE and spacer thickness, we can achieve efficient side lobe suppression in the behavior of the diffraction efficiency, as a function of both incident wavelength and angle.

The structure evolution characteristics of single and stratified NdF3 optical thin films on amorphous quartz substrates have been investigated by cross sectional transmission electron microscopy, x-ray diffractometer measurements and atomic force microscopy. The films were deposited by physical vapor deposition under ultra high vacuum conditions. The morphology changes with substrate temperature from V shaped columnar (Zone T) to a columnar morphology corresponding to zone II. The zone boundary falls in the range above 300 °C. The surface roughness of the single films is lowest at 300 °C substrate temperature. The main texture components are <111<, <1 13< and <001< respectively for the three single films of increasing substrate temperature. The surface roughness is decreased by the stratification. The grain size is increased by stratification with CaF2 and decreased by stratification with MgF2 compared to the grain size ofthe single film at the same substrate temperature. Keywords: thin film, stratification, morphology, texture, surface roughness, extinction

Theoretical insights are developed for modeling the interaction of microwave radiation with conductive and magnetic thin films on dielectric and semiconductor optical substrates. A software program has been written to analyze the transmission, reflection and absorption of these multilayer stacks. Results from computer analysis illustrate methods which increase the shielding effectiveness over simple conductive layers of grids or meshes. Additionally, these multilayers can be designed to absorb rather than reflect, microwave radiation at specific frequencies.

Chalcogenide alloys Sb_xSe_y are being applied to phase-change, reversible optical storage. The non- stoichiometric compound are researched displaying their interesting phenomena before and after anneal in a furnace, which were characterized by the X-ray diffraction technology. The composition of the Se richer than Sb will result the film in amorphous state in the room temperature evaporation. The Sb₂Se₃ crystallized out from the non-stoichiometric alloys have the lower crystallization temperature compared with the stoichiometric alloys Sb₂Se₃. Double layers consisting of Sb film deposited on Se film was investigated which revealed its special characteristics. The sublimation and the diffusion of the atoms during annealing in the lower temperature have the important effects on the material's crystallization behavior, the great kinetic energy of the atoms will result in the crystallization of Se and Sb₂Se₃ and, the lower crystallization temperature is just what we expected in the laser recording and for the optical-data storage. An important conclusion can be made from the experiments, the crystallization can be finished by adjacent atomic diffusion. The reason for optical crystallization is also discussed.

The three transition metal nitrides TiN, ZrN and HfN have remarkably high stability due to their bonding: a mixture of covalent and ionic contributions. The optical properties of these nitride compounds are free-electron like to a surprisingly large extent, in particular in comparison with the corresponding carbides. It is argued that the interband optical excitations of the d-electrons are restricted by selection rules, resulting in a Drude like behavior of these d-electron compounds. Hitherto, one of the main optical applications has been as opaque, wear-resistant replacements for gold-coatings. This review includes the efforts to study, understand and enhance the optical selectivity of group IVB transition metal nitrides as the selective surface in high temperature thermal solar absorbers, as the metal layer in LE-coatings on energy-efficient or solar control windows and as a Langmuir probe coating. The reflectance edge is not in the optimum position for absorber applications and attempts to shift it with alloying were unsuccessful. Recent development of inhomogeneous, cermet- type nitrides hold some promise. The LE-coatings will not reach as high selectivity as the current noble metal based multilayers, but many find use in aggressive environments because of their excellent stability.

Ion beam sputtered SiO₂ and TiO₂ optical thin films are investigated. The optical properties absorption, light scattering and refractive index and the mechanical properties thickness, density and stress are studied directly after deposition and the posttreatment by isochromal annealing up to 300 degree(s)C. Absorption losses of SiO₂ single layers decrease under annealing. The corresponding extinction is reduced below 1 X 10^-6 at 514 nm. The dynamics of this process is investigated. The density which is higher than bulk density decreases, while the thickness increases. TiO₂ single layers show a more complex behavior under postannealing. At higher temperatures this behavior is dominated by crystallite growth in anatase and rutile modification. Compressive stress is reduced. The single layer results of both materials are compared with those of double layers and Fabry Perot multilayers. Differences in absorption are discussed. In double layer systems, lowest bulk extinction of TiO₂ is estimated with 1.5 X 10^-5 at 514 nm. An irreversible peak shift of Fabry Perot filters after annealing comes from changes in thickness and refractive index. The overall performance of multilayer systems can be improved by an adapted annealing procedure.

Stress in thin films deposited by Reactive Low-Voltage Ion Plating is studied in air and at room temperature. A multilayer stack, composed of tantalum pentoxide and silicon dioxide layers, is considered and the interactions layer to layer turn out to have no effect as regards to the final bending. Evolution in stress after annealing shows the possibility to reduce the stress as well as the absorption for tantalum pentoxide thin films. Finally, ion implementation, such as helium and xenon, at high energy, prove to be also a way to vary and diminish the stress in thin films.

Properties of single-layer and multilayer Al₂O₃/SiO₂ coatings deposited by Plasma Ion Assisted Deposition (PIAD) and Low Loss Reactive Evaporation (LL-RE) have been studied with emphasis on their use in the UV and VUV spectral region. The influence of significant deposition parameters, mainly the bias voltage in the case of PIAD and the substrate temperature in the case of LL-RE, on the optical and structural properties as well as on the film stress is investigated by spectrophotometry, IR- spectroscopy, light scattering, atomic force microscopy, and laser beam deflection stress measurements. Laser photon interaction with single-layer films and multilayer coatings was studied for the different wavelengths of excimer lasers (ArF (193 nm), KrF (248 nm), XeCl (308 nm) and the 3rd harmonic (355 nm) of the Nd:YAG solid state laser. High laser damage resistance and environmentally stable optical characteristics have been accomplished for multilayer coatings, especially for KrF (248 nm) excimer laser. The influence of the surface roughness of the substrates on the surface topography and the related scatter losses of the coatings has been investigated by integrated light scattering and atomic force microscopy measurements.

Plasma-IAD with the APS (advanced plasma source) has been introduced into the market in 1992. Up to now this technique is used worldwide in almost 100 coating systems. A large number of different layer systems has been investigated in R&D and applied in production. For ophthalmic applications plasma-IAD with the APS is used for antireflection systems as well as for wear resistant coatings onto organic substrates. New processes which combine the AR coating and the hardcoating on ophthalmic lenses have been successfully introduced into mass production. Plasma-IAD is also used for laser protection coatings onto plastic substrates. The ability for the production of shift free multilayer coatings is utilized in manufacture for many applications such as steep edge filters for color separation, rugate filters for laser protection, narrow-bandpass filters in the NIR region for wavelength multiplexing in the field of fiber optic communication or for radiometers in the UV-B region. A review of the development of some important APS based coating processes and applications shows the flexibility of plasma-IAD with the APS. Actual evaluations of the optical constants of Ta₂O₅ layers deposited with APS assistance show a low extinction coefficient and a stable refractive index. New results of the performance, temperature behavior and long term stability of some interference filters confirm high packing density and low absorption of the films produced with plasma-IAD. The result of a reproducibility experiment demonstrates high process stability and high monitoring accuracy.

A comparative study of different ion and plasma assisted physical vapor deposition processes at low temperature is reported. To work out a clear comparison of the different processes, the object of the study are single layers of different metal oxides like Ta₂O₅, TiO₂, SiO₂ and mixed oxides like H4 (Merck) deposited on glass and silicon substrates. Three different types of ion- (or plasma-respectively) sources are used: the cold cathode ion source from Denton (CC 104), the end hall ion source Mark II from CSC and the advanced plasma source from Leybold. Each of these processes is run under conditions concerning process parameters like bias, ion current, ion energy, beam characteristics and gas flow, which were understood to be optimized also to maintain long-term stability as realistic production conditions. The resulting metal oxide single layers are characterized by their optical properties, dispersion curves for NUV and VIS as well as absorption and scatter at discrete wavelengths. Also discussed are mechanical properties like hardness and adherence. A test method is presented which clearly shows the superior behavior of the IAD coatings.

Fabrication of high performance optical filters are typically long deposition runs. Successful deposition requires the monitoring and correction for long term process variability due to source depletion and equipment degradation as well as control of immediate parameters such as deposition rates and substrate temperature. Multiple resolution analysis of insitu sensor data using wavelet transforms provides the means of extracting both short term and long term trends from a common data stream. This paper presents a method for monitoring the fabrication of discrete and Rugate filters using the Haar transform. This technique begins by describing the average of the time series, and then successively resolves the time series into more detailed layers. The lowest resolution coefficients describe optical density growth and absorption. The more detailed layers describe systematic and periodic variations due to the growth of optical thickness. Separate analysis of data for different time regimes provides insight into different physical parameters. Least square fit to the low order terms relate to parameters such as film absorption and growth of optical density. Windowed Fourier transform of periodic structure in the coefficients of the detailed layer provides insight into a number of performance parameters such as the period and amplitude of the optical thickness cycle which is characteristic of Rugate design.

A VLSI fabrication technique by using LPCVD to deposit polysilicon films and then reoxidized it back to specific oxide and polysilicon multilayer stacks has been studied and evaluated. Thermal oxide films are much more stable than PECVD oxide films both in optical and electrical response. Also, the NOX films has been examined and simulated for the related purpose.

A durable Interference Filter for 1.65 (mu) with peak transmittance of above 90% is shown. The filter consists of Si and SiO₂ layers on glass, with a SiO₂ top layer for additional durability. Applying on the other side of the substrate an edge filter (long wave pass filter) with the same materials, resulted with a large blocking spectral region, without the use of an absorbing glass substrate.

High strength/weight carbon fiber-reinforced composites (CFRCs) are finding applications where control of surface infrared emission or reflection is desirable. A quarter wave sputtered Ge film has been shown to reduce the normal emittance of a bismaleimide CFRC in the 8 - 14 micrometers band by 39%, with angle dependence theoretically constant out to 80% off-axis. A three-layer HLH stack is predicted to reduce emittance of less than 0.1. For thermal IR polymer curing, a single-layer coating optimizing emissivity in the polymer's absorption band while suppressing emission at longer wavelengths may yield electric power savings in the 10 - 20% range.

For optical systems special anti-reflection coatings can be designed which reduce the reflectance for a high number of glasses at normal and non-normal incidence (multi- configuration). In that way, all lenses of a lens system can be coated with the same coating design. The results for single wavelength (laser) applications as well as for broadband applications will be discussed. Furthermore, the application of these coatings in several lens designs will be demonstrated. For this, transmissions are calculated in an improved optical lens design program (WinLens). The transmission performance of complex lens systems is listed surface by surface and is graphically displayed for the optical axis and for all chief rays and therefore for all main angles of incidence. Experience about these new coating designs combined with new features in an optical design software provides new aspects about `re-design to cost' for the lens designer.

A fiber-optic pH sensor is demonstrated using thin film Langmuir-Blodgett (LB) films to form a single-mode planar waveguide, evanescently coupled to a side-polished single- mode optical fiber. The LB technique shows two distinct advantages in the fabrication of such sensors, the ability to control the overlay waveguide thickness to a single molecular layer (approximately 3 nm) and also, as the materials used are organic, the ability to engineer specific materials for different sensing purposes. The response of the sensor is also investigated through changes in the overlay refractive index, caused by changes in its absorption spectrum via a simple Kramers-Kronig model. The model is shown to be able to predict the response of the sensor.

The principles and chief properties of optical reflection and transmission filters based on guided-mode resonance (GMR) effects in multilayer structures comprising gratings and homogeneous thin films are presented. Detailed fiber characteristics (center wavelength, lineshape, and linewidth) are calculated using rigorous coupled-wave analysis for TE and TM polarized incident waves. These filters exhibit desirable characteristics such as high resonance efficiency with narrow or wide linewidths. Near- zero reflectance sidebands over extended wavelength ranges are obtainable using multilayer waveguide-grating structures. To illustrate the potential of this technology, calculated GMR reflection and transmission example characteristics are presented for filters made with common thin-film materials operating in the visible spectral region. Excellent reflection-filter features are found when antireflection conditions prevail away from the resonance wavelength. The transmission filter is optimized when the structure is highly reflective off resonance. It is found that long-range, low sidebands are obtainable for a single- layer GMR filter with a TM-polarized plane wave incident at the Brewster angle. GMR filter fabrication tolerances are briefly discussed. A calculated example illustrates the sensitivity of the filter center wavelength to variations in layer thickness. The effects of absorptive loss are treated. It is shown that, in general, GMR filters suffer loss- dependent wavelength shifts such that the reflection peak occurs at a different wavelength than the corresponding transmission notch. However, under antireflection conditions, the resonance location becomes insensitive to loss. Finally, reflective GMR thin-film structures that support multiple waveguide modes are studied. These devices exhibit characteristic angular and spectral signatures with unique appearance.

Cut-off filters reject all the radiation below and transmit all the above a certain wavelength and vice versa. In this paper, we will study the design and fabrication of a short wave pass or a long wave pass dichroic mirrors for color separation and recombination from the R.G.B. color beam source. In the laser display system, color separation and recombination is very important. We designed the coating layers so that the best performance may be obtained from a 45 degree incident s-polarized light. The following fabrication specification is satisfied in our color separation/recombination of the Kr-Ar laser source. The first dichroic mirror for the blue color separation, maximized on reflectance and transmittance as R > 99% in the blue regions (400 approximately 490 nm) and T > 90% in the green and red region (510 approximately 700 nm). The second dichroic mirror for the color recombination maximized the reflectance and transmittance as R > 99% in the range of 510 approximately 700 nm and T > 90% in the blue color region. In the third dichroic mirror for which it used the color separation and recombination of the green and red simultaneously, maximized the reflectance and transmittance as R > 99% in the green region (510 approximately 560 nm) and T > 90% in the red region. These fabricated mirrors were applied in our laser display projection system. We obtained an excellent result.

Granular gold and nickel films were prepared by thermal vacuum deposition onto glass substrates. Optical transmittance at near-normal incidence was recorded as a function of the relative mass thickness on each side of the percolation threshold. We show that our transmittance spectra may be described within the framework of Bruggeman's symmetrical approximation for the effective dielectric function with some modifications.

Optical properties of ultrathin aluminum quantum wells deposited on glass (SiO₂) and crystalline silicon (a-Si) are studied at room temperature in the infrared region at 9.201 micrometers wavelength within two thicknesses range: d approximately 5 to 35 angstroms and 36 to 112 angstroms. All our thickness dependence reflectivity measurements were made by tuning a CO₂ laser to 9.201 micrometers for p-polarization and an angle of incidence of 7 degree(s). Our main contribution here is the reveled fine oscillatory behavior on a gradually increasing reflectivity spectra. These fine oscillation structure can be attributed to quantum size effects.

Narrow-band polarizing interference filters make the new category of thin layers construction. Due to the compact trends the narrow-band polarizing interference filters eliminate one of two elements used traditionally on separate substrates: narrow-band filter and thin layer polarizer. Considering them as narrow-band interference filters it is possible to project their parameters such as center wavelength or the half bandwidth. The choice of the narrow- band polarizing interference filters design is controlled by the polarizing degree.

We present experiments on the optical properties of ultrathin (a few nanometers thick) films (copperphthalocyanine, amorphous silicon) with an incorporated metal cluster film (silver, indium). Due to the spatially close interface, the plasmon absorption may be displaced from its resonance frequency in the bulk, and its average position may be controlled by the average thickness of the ultrathin optical film. For example, we observe a shift of the plasmon resonance of silver clusters in amorphous silicon films (on quartz glass) from 440 nm to 740 nm, when the silicon thickness increases from `zero' up to 15 nm. The deposition experiments are accompanied by investigation of the film structure, particularly in order to estimate the silver cluster diameter, which is around 3 nm or less. Additionally, numerical simulations are in progress to optimize the island film preparation conditions.