The two main synthesis methods of optical interference coating design, Epstein equivalentlayersynthesis andChebyshevpolynomial synthesis, areevaluated, characterized and compared. Epstein designs are easier to produce. Chebyshev designs are superior but, because of implementation problems, often turn out worse than Epstein designs. This could change in 1 ight of recent progresses in rf-sputtering.

A method for designing thinfilm optical filters based on simulated zone melting techniques is outlined. In contrast to conventional methods, but like all methods based on the simulated annealing ideas, it does not require a good starting design and helps to find good solutions separated by barriers in the quality function. Recently, there has been a lot of interest in mosaic filter arrays, which are required for colour cameras based on a single charge coupled-device image sensor. As a result of the trend to smaller and higher resolution sensors, the pixel size becomes smaller and therefore the thickness of such filters significantly affects the cross talk from pixel to pixel. Such constraints can be incorporated in the merit function by penalizing too thick dielectric layers. It turns out that the thickness of typical colour separation filters can be kept significantly below 2gm, using as dielectrics T102 and S102. Examples of yellow, green and cyan filters, as well as a spectrally Gaussian transmission filter are presented.

The fully-automatic design of multilayer optical systems is an important task in thin-film technology. This paper presents a new (stochastic) synthesis method, which supplies the optimal design without requiring any sort of designer's experience. It is essentially based on the mixed use of Montecarlo techniques and descent optimisation algorithms. Some preliminary results show the capabilities of this method, which is yet in progress.

The dependence ot permittivity of coating on its thiclrness determines merit ftnction related to the problem or synthesis of optical coatings. From mathematical point of view, synthesis problem can be regarded as a specIal kind cf extreme problems. Theorems, which provide optimum conditions for synthesis prooedure, have been obtained. Taking into account these theorems, one can deduce that at normal incidence optimum optical coating appears to he double-component. Based on the results and principles of optimal control theory, special synthesis methods were elaborated. These methods don't use any starting design.

The NRCC Fourier transform synthesis method has been applied for the first time to an optical thin film design problem in which the external media are different. Graded index AR coatings for germanium substrates have been synthesized and compared to multilayer solutions. No limits have been imposed on the refractive indices. Although such systems cannot be put into practice, they provide basic insight into the general nature of broadband AR coatings. Admittance diagrams have been calculated for some of the systems to gain further understanding of their behavior.

ManY works have been devoted to theoretical treatment of analysis and sYnthesis of superfine stratified periodic structures because of their importance for successful solution of numerous Problems of fun dainental and applied phYsics. Hitherto several methods have been develoPed quite well and results have been generalized rather completelY, which refer to periodic structures consisting of laYers with optical thickness of a quarterwave, half-wave or so, However, it is the Progress in modern PhYsics and engineering (for example, the intensive development of the previouslY PoorlY studied region of the electromagnetic spectrum, namely: the medium and far IR). the necessitY to solve diagnostics Problems of stratified non-uniform media (with a non-uniformitY Period being less than the wavelength) that make it necessary to carry out both analYtical and numerical analYsis of the ProPerties and peculiarities of stratified structures with superfine laYers much less than the wave- 1 ength, In recent Years a member of works have been Published which grove the possibilitY to sYnthesize such structures in order to solve problems of improving optical properties of the interface between two media and to describe basic Properties and peculiarities inherent onlY to this class of structures18. It is in the context of such statement of the Problem that we shall Perform a generalized analYsis of proPerties and various peculiarities of the superfine stratified structures in the Present Paper.

CADCAM system is very vital in the development and production of high efficiency optical coatings, in which in-situ analysis and optiniizatfrxi is the nucleus. A new algoritlin for in-situ analysis and optimization of coatings has been proposed, which has provision for precise determination of optical parameters, namely refractive index n, and gearetrical thickness d, of any layer :tt the multilayered configuration and, to account for adverse effect of the deviaticxs in the optical pareters through global re-optimization of the coatings. It has been implemented on 8086/8087 microprocessor systn in which 8086 is a 16 bit microprocessor and 8087, a coprocessor for high speed floating point operatixs. The validity of the algorithn has been established through a wide range of hypothetical case studies and experimental deve1opint of a few coatings such as wideband antireflecticx coatings (ARCs).

The inclusion dominated model of laser-induced damage is reexamined in order to explore the consequences of recent measured low values of thin film thermal conductivities. In the model absorption of radiation is assumed to only occur in the inclusion via Mie scattering. From the analysis two different values of the imaginary part of the index of refraction are predicted for a given damage threshold. Physical mechanisms are proposed for each value. Interestingly, varying the thermal conductivity of the both the host and inclusion over several orders of magnitude seem to have a less than expected influence on the damage threshold. However there is also proposed an effect of the index of refraction associated with a given damage threshold which is based upon two distinct absorption mechanisms. The results of this modified model are then compared with experimental data for damage thresholds of different thickness films.

We show how the anisotropy of scattering enables to point out the origin of microroughness in optical coatings with no ambiguity. Experimental results prove that residual roughness due to material microstructure is negligible with coatings produced by Ion Assisted or Ion Plating deposition. In these conditions, and provided that the substrate is measured before coating, prediction of scattering from a stack of any design requires the knowledge of only two cut-off frequencies that describe the action of materials at interfaces. These parameters can be determined with single layers and then can be used for more complex optical systems. Since isotropy degree variation of scattering does not depend on the design of the coating, it enables to show that the differences that can occur between calculation and measurements are due to thickness or index errors on the layers. Therefore the substrate roughness plays a primordial role and we compare, using numerical calculation, the roughness spectra that can be obtained with mechanical or optical measurements.

Photothermal deflection has been used to map the absorption characteristics of thin film optical coatings. Our experimental set-up can give low level absorption coefficient down to 1 ppm, with a spatial resolution limited by the excitating laser beam diameter (100 tim). On single layer films, we can calculate extinction coefficient of the deposited material with a detectivity of a few i07. We present a study of absorption losses in single layer titania films and in TiOWSiO2 Fabry-Perot filters prepared in our laboratory by electron beam evaporation, ion assisted deposition and ion plating. Local variations of absorption on the sample surface can be very large especially in lowly absorbing samples; high absorption sites may be related to local defects responsible for laser damage. Furthermore, we show that some titania films can present photoinduced instabilities. Photothermal deflection spectroscopy is a good way to study absorption evolution under illumination. In Ti02/Si02 Fabry-Perot filters, we have observed that these absorption changes are associated with important drifts of transmission curves. So these instabilities can be explained by a change of the value of the complex index Ii = n - ik. Results lead to the conclusion that stability under illumination is strongly correlated to the deposition technique and also to the deposition conditions: unstable samples are mostly prepared by electron beam evaporation.

The infrared properties of most oxide films are dominated by the effects of the lattice vibrations which are well represented by a model of superposed classical oscillators. In this model, the complex dielectric constant is a function of one or more classical oscillators hosted in a dielectric medium. Each oscillator is specified by its strength, resonance wavelength, and linewidth or damping. Evaluation of the oscillator parameters takes advantage of the observation by Berreman that a thin film has a strong absorption band for p-polarized light at oblique incidence at the wavelength for which the dielectric constant is zero or nearly zero. Each absorption band corresponds to a lattice vibration band which is represented by an oscillator. The p-polarized transmittance at 45° incidence of 0. 1 micron thick films of iron oxide, silicon oxide and silicon nitride was measured. These data were fitted with dispersion models composed of superposed classical oscillators. The results indicate that the properties of silicon oxide and iron oxide films are each modelled by three classical oscillators hosted in a pure dielectric medium. Similarly, the silicon nitride results are represented by two oscillators.

Electron beam evaporation and ion assisted deposition have been used to prepare BaF2, LaF3 and HoF3 single layers. These fluorides were chosen as low index materials for laser applications at 10.6 Lm. The films were characterized by Rutherford backscattering (RBS), x-ray diffraction, scanning electron microscopy (SEM), stress measurement, laser calorimetry, and spectrophotometry. The influence of substrate temperature, deposition rate, ion energy, and ion to molecule arrival ratio on film growth was analysed and related to the optical properties. Although each material reacts differently to the deposition parameters, ion assisted deposition leads to an increase of the absorption loss at the laser wavelength for all three materials.

Photothermal Deflection Spectroscopy (PDS) is a recently developed technique that is finding a useful application in the measurement of low optical absorptance of thin films. Among the noise sources affecting the PDS measurement, probe beam pointing instability and mechanical vibration play a considerable role. In this work an optoelectronic system for the reduction of their influence is described. Moreover, PDS measurements are typically performed keeping the sample immersed in a deflecting liquid; thus measured values of absorptance must be corrected when other surrounding media, as air, are considered. This correction is an easy task for single film coatings. Here the general case of an unknown multiplayer coating is analysed; a range of values containing the true absorptance in air is obtained by theoretical analysis and a practical method to evaluate the absorptance in air is discussed. Finally, deflecting liquids alternative to the commonly used CCI4 have been examined. Useful optical range, thermal diffusivity and “relative deflecting power” of CCI4, CS2, Iso-octane and Aceton are reported.

The optical characterization of thin films is a field of continuous investigation, nevertheless there is a lack of data of refractive indexes (n-ik) in the infrared spectrum. In this paper a method for the determination of the optical parameters n and k is described that starting from spectrophotometric measurements gives, by computer, the refractive index profile in a wide wavelength range. Y203, Al203, HfO2, ZnSe and ZnS are the examined film materials and their n and k values in the visible and infrared spectrum (0.35-20 m) are reported.

In situ ellipsometry is of interest for monitoring and control of growing films. Its extreme sensitivity to thin layers also allows the measurement of the interface film frequently formed between a growing film and the substrate. The installation and operation of an in situ system on two different vacuum coating machines is described. The system records 'F and measurements every 5 seconds during film growth. We present an algorithm for computing the thickness (d) and index (n'.ik) of a growing and an interface film on a known substrate from five Y and measurements at different times during film growth. Numerical solutions of the ellipsometer equations for d, n, and k performed using a 25 MHz 80386 microprocessor with an 80387 math co-processor require about 30 minutes. Additional solutions beyond the first five data sets require only two additional measurements. By taking data in repeated time intervals during the growth of a film, we obtain a depth profile of its optical properties.

Surface roughness of a fine metallic film. i.e.. mirror finished. has been determined by a Scanning Tunneling Microscope (STM). The mean value o the roughness is measured based on STM images of a three dimensional line plot of the surface profile. The technique is found capable of determining the roughness in a nanoscopic scale, lO m. Such technique is used in the present work to measure the roughness of various thin films ( 1 5 tm) in amorphous and crystalline structures.

Modern optical systems require still higher quality optical coatings. Conventional production techniques are not able to give such high quality layers. One of the main defaults comes from the relatively porous structure of the thin films; as a consequence the sensitiveness of the materials to the moisture gives noticeably unstable properties versus time. In this work, after a very short review of the different techniques nowaday used to perform high quality optical thin films, we will be especially interested in oxide layer production (Si02, Ta2O5, Ti02). To give a good comparison of the performances obtained with techniques such as TAD and ion plating we need extremely powerful characterization means: - In vacuo measurements of optical properties allowing the study of spontaneous water adsorption during air entrance; - Absorption measurement with photothermal deflection spectroscopy; - Scattering losses measurements and consequently determination of the grain size of the microstructure. Refractive index measurements, and optical anisotropy determined by guided mode study. Finally some views from electron microscopy justify the validity of the model used with our characterization techniques. To end, we will show the interest of ion plating technique when we are looking for very uniform deposition on large surfaces.

Trends in optical thin film interference filters have created an increasing demand for the production of high tolerance designs for a wide number of applications. Much has been achieved by conventional filter designs but more novel structures such as distributed Bragg filters (DBR) and rugates are of increasing interest. Such filters require a highly controlled deposition technology as many of the constituent layers are only a few tens of angstroms thick. At this previous conference (Hamburg 1988) the potential of molecular beam epitaxy (MBE) was discussed with reference to the manufacture of such demanding structures. Although MBE equipment is usually associated with the epitaxial growth of IIIV semiconductor material, the application has lead to the the availability of a wide range of ultra high vacuum (UHV) equipment suitable for the deposition of optical thin films. To date, considerable development has taken place with the commissioning of e Vacuum Generators V9OH production GaAs machine, adapted for optical thin film fabrication. This unit has a single 4" substrate capacity or multiples of smaller dimensions. Film thickness uniformity of better than +1- 0.5% have been routinely achieved over the maximum substrate area using a single rotation. Materials under current study include ZnSe, ZnS, BaF2 and PbF2. These offer candidate low and high index pairs from the UV to the IR region of the spectra and have been shown to be compatible for incorporation in a single chamber environment with minimal cross contamination. In this paper, current results will be presented from this unique deposition facility with particular emphasis on the gains made in depositing highly complex multilayer structures. An assessment will be given as to the potential of molecular beam deposition (MBD) as a production technique.

A new sputtering technique (PLISD: Pulsed-Laser Induced Sputtering Deposition) for thin film deposition is reported. Instead of the glow discharges of usual sputtering processes, PLISD uses a pulsed laser and an electrically conductive target for the generation of the bombarding ions. Its features and possible advantages are indicated, among which is the possibility to carry out sputtering deposition in a high-vacuum environment. Some preliminary experimental results are given which demonstrate the feasibility of the PLISD technique.

Ion assisted deposition (lAD) is a well known technique to iniproye the properties of thin films. A wide range of materials and conipleted layer systems have already been investigated by many laboratories. One disadvantage of this technology is the small useful substrate area compared to conventional thermal evaporation. This is due to the limited ion beam size of the available ion sources. Therefore we have developed a new plasma source which is able to irradiate a substrate holder of 800 mm diameter with high plasma current density. The principle of operation and some details of the plasma source are described. The experiments were done in a conventional coating system. The plasma source has been operated at up to 90 V discharge voltage and up to 80 A discharge current. Up to now we have deposited some single layers with dielectric materials. For TiO2 we have achieved an refractive index of 2.55 at 550 nm.

After fairly extensive discussions of the advantages and disadvantages of low energy and high energy ion beam bombardment of a growing film, we review briefly a number of experimental results obtained with various samples made with low voltage reactive ion plating deposition. The availability of a state-of-the-art high vacuum coating machine specifically equipped for this process is the foundation for a major leap toward achieving near-perfect optical coatings. The high density of ion plated thin films makes them impermeable to water vapor and corrosive solutions. This has been demonstrated with protected aluminum mirrors, polarizers, and infrared anti-reflection coatings. An indication of the high packing density is the substantially higher refractive index than that of comparable layers deposited with either conventional electron beam evaporation or ion assisted deposition. The spectral transmittance of multilayer stacks of oxide thin films is lower than expected from theoretical predictions which assume absorption-free dielectrics. The observed absorption is primarily of an interface nature rather than a volume effect and occurs predominantly in combinations of Ti02 and Si02 thin films.

Reactive RF planar magnetron sputtering has been used to deposit thin films of vanadium dioxide onto silicon and germanium substrates. The present work demonstrates the feasibility of reliably reproducing stoichiometric material by this method. The films exhibit a sharply defined transition in optical properties. The temperature over which the transition occurs is examined. Attention has been given to determination of the structure of the vanadium dioxide and the relation to the switching properties. X-ray diffraction techniques were employed to assess structural purity. Fine surface texture has been evaluated using a high resolution stylus instrument and some relation to optical scatter loss is made. The optical transmission of an enhanced transmission thermal switching device incorporating a vanadium dioxide film is reported.

The problem of modifying the intensity spectrum of a given source in order to obtain a required intensity curve is discussed. The special problem of the correction of a tungsten lamp of color temperature 2856 K in order to match AMO solar spectrum is considered, taking advantage of a new method for the layout of glasses and multilayer combined filters. The results presented here show that a structure composed by two glasses and 13 layers allow to solve it with a limited loss in intensity.

System aspects of filter radiometer optics used to sense planetary atmospheres are described. Thus the lenses, dichroic beamsplitters and filters in longwave channels of the Mars Observer PMIRR Pressure Modulator Infra Red Radiometer instrument are assessed individually, and as systems at 20.7 tim, 31.9 tim. 47.2 m wavelength. A window filter and a longwave calibration filter of the SCARAB earth observer instrument are assessed similarly.

In numerous instances a ray propagating through an optical system penetrates a multilayer coating such a bandpass filter, polarizer, beamdivider or antireflection coating. The additional retardance that the coating adds to that ray is, to a first approximation, the optical thickness of the multilayer. Several examples are given.

This paper contains the results of the theoretical and experimental investigations of the light diffraction on the gratings on the layered coatings. The theoretical expressions for the diffraction intensities for some practically important cases are obtained.Discussion is focused ()fl the problem of using theoretical results for control and measuring parameters of the diffraction gratings and thin films.

Various optical elements with Gaussian and super-Gaussian transmission or ref lection characteristics are used both inside the laser cavities to create a good mode discriminatio?,2and outside them to avoid Fresnel diffraction ripples in beam cross section, e.g. ' (review papers). The frustrated total internal reflection amplitude filter or so-called apodized aperture (FTIR AA) is one of these devices. In this paper we describe the ETIR AA which is a glass cube consisting of two right-angle prisms with their hypothenuse faces near the optical contact, separated by the single dielectric film with smooth monotonous variable thickness along the cross-section. Close to spherical and different smooth flat-top shape surfaces which are Si02, SiO or MgF2 single profiled films with'O.5-1.5pm maximum value of thickness were deposited on glass or quartz substrates by electron beam, reactive heating or sputtering techniques. The comparative analysis of rotating mask and noncontacting mask methods for preparation of profiled films has been carried out. The results of testing of such filters in lasers and laser radiation damage thresholds of films in optical contact conditions are presented herein.

A highly sophisticated antireflection coating and a cut-on-filter - designed by the Leitz program "RDP" - will be pointed out. The program runs on a VAX 8530 and allows to calculate reflectance, transmittance and phase of randomly polarized light which interacts with marginal surfaces. The number of layers is not limited. Some or even all layers are allowed to be anistropic. Up to four layers may be inhomogeneous both in refractive indices and absorption constants. At a time two thicknesses, two refractive indices and absorption constants as well as the angles of incidence may be varied independently in each run. The calculated values will be compared with the results of measurements. The antireflection coating is evaporated in a Balzers high vacuum evaporation plant, controlled by the process unit BPU 420, whereas the cut-on filter is evaporated in a Leybold box coater with Leycom III and two electron-beam guns.

The residual reflectance colors of broadband antireflection coatings for ophthalmic optics have been investigated as a function of statistical production errors, lateral thickness changes and incidence angle of light. The goal was to design coatings with good production stability, low lateral color variation even over steeply curved lens surfaces and low angular color shift. The investigations show that the final design can only be a compromise between the different requirements.

The emission distribution characteristics of an evaporation source can be used to defme the correct geometry in the vacuum chamber for the production of uniform-thickness coatings. We first measured the thickness of coatings on test pieces positioned at known radial distances on a single rotation flat rack in the vacuum evaporation chamber and used these data in a computer program which found the source emission function, in the form cos° , which provided the best fit to the data. is the emission angle of the evaporant stream from the source, measured from the vertical. The known emission function was then used to determine the source offset and calotte curvature which produced the best thickness uniformity over the diameter. In one example, we found 0 = 131 for A1203 evaporated from an electron beam source. This enabled us to predict a chamber geometry which yielded coatings across a calotte of diameter 81 cm with a thickness variation of 0 = 1.70, but the uniformity was less excellent (±3%) because this material is difficult to evaporate controllably. The technique is a powerful one for anyone setting up his coating chamber to produce a large number of coated substrates.

The limiting thickness uniformity attainable for the coating of multiple substrates inside a thermal evaporation physical vapor deposition (PVD) unit is theoretically analyzed. This study compares the classical spherical (dome-shaped) calotte with a plane sectors reversible lens holder setup. This arrangement is very useful for two-sides substrate deposition, such as antireflection coatings on lenses. The design of static correcting shutters for this kind of configuration is also discussed. Some results of this theoretical study are presented.

Reviewed are the approaches for the determination of the optical constants - refraction indices, absorption coefficients and thickness of thin uniaxial film with various optical axis orientations, arbitrary among them. The comparative analysis of various measurements - MAI (multi angle of incidence ellipsometry), MTE (multi film thickness ellipsometry), IHE (multi immersion ellipsometry) and MOE (multi orientation ellipsometry) and corresponding techniques for solving the inverse task is given for each type of optical axis orientation.

The most specific feature of thin i1m deposited in vacuum is there columnar structureI2. The investigation or its impact on the process of penetrating of electromagnetic waves turns to be the main goal of the present paper.

For high power laser applications, extinction coefficients and refractive indices of ion beam sputtered resp. ionplated Hf02-, Si02- and A1203- films were determined by spectrophotometric analysis in the wavelength range between 200 and 500 nm. Film qualities were related to the corresponding process parameters. Qualitative information about water content has been obtained by infrared spectroscopy. Impurities and film stoichiometry were determined by RBS analysis. Laser induced damage thresholds were measured with a (KrF*)excimer laser at 248 nm. The tested samples were single layers as well as high reflecting QWOT stacks. All results were compared with the corresponding values of e-beam coatings.