Nonlinear optical processes have received international attention because of their importance in optical signal processing and computing. Organic molecules and polymers form an important class of nonlinear optical material. This paper discusses the basic relevant concepts in the newly emerging area of nonlinear optical processes in organic molecules and polymers. It provides the results of a comprehensive study in this area being conducted in my laboratory. This study includes theoretical calculation of microscopic optical nonlinearity; design, molecular engineering and synthesis of novel organic structures; experimental investigation of nonlinear processes using picosecond and femtosecond laser pulses; and the study of device phenomena. At the end, the current status of this field and future directions of research are discussed.

The objective of this paper is to discuss practical aspects of pumping systems typically used in precision optical coating systems. The paper is directed at thin film technologists, engineers and technicians and will only touch lightly on vacuum pumping theory. We shall provide data from actual production systems that can be a useful guide to purchasers of optical coating systems on how pumping systems should be configured. We will also attempt to identify common problems relating to specific pumps and processes that users should anticipate and avoid.

(A1 1-x Si x )0yNz films have properties which make them desirable as durable overcoats and corrosion barriers in optical thin film structures. (Al, Si )O N films were reactively DC sputtered from Al, Si targets (x = 0.0, 0.117, 0.30) in Ar/N2/O2 atmospheres. Nitride films had sputter efficiencies three times that of the oxides and ESCA analysis of the films showed that the film composition varied non-linearly with reactive gas ratio and sputter rate, incorporating more oxygen than nitrogen for a given gas flow. This behavior is correlated with the hysteresis curves for the oxide and nitride states. Optical properties of the films were also found to vary with index dropping disproportionately to the 0/(0+N) flow ratio, but linearly with the ratio of atomic percent of 0 and N in the films. Durability properties of (A1 1_x Si x)0 NZ films were tested at several compositions. It was found that with high nitrogen context the wear resistance increased with Si content and the oxides were generally less wear resistant than the nitrides. The corrosion resistance also increased with Si content, but in this case, the oxides were generally more stable. Film stress became more compressive with 0 and Si content. Analysis of ESCA binding energy data indicates that the Si forms alumino-silicate bonds in the film, which apparently contributes to the durability properties.

Ion Beam Sputter Deposition (IBSD) was proven to be a useful technique for producing high performance optical coatings. However, compared to other deposition techniques, several problems remain to be solved, such as low deposition rates, small areas with homogeneous deposition rate and the problem of contamination. In the work described here, a cubic vacuum chamber has been equipped with a commercially available ion beam source, a triple stage target holder and a rotating substrate holder. The primary interest was to get a reasonable deposition rate over a sufficiently large area. Single layers of SiO2, Ta205 and TiO2 and multilayers of Si02/Ta205 were produced. Contaminants in the films were analyzed by various techniques mainly by Total-Reflection X-ray Fluorescence (TXRF). Optical properties of the coatings were investigated to study the influence of the contaminants on the performance of the optical coatings. The optical properties were characterized by the refractive index, the absorption coefficient and the scattering behaviour. Scattering losses were measured by means of Total Integrated Scattering (TIS) and Angle Resolved Scattering (ARS). The damage threshold against high-power laser pulses of 1.06 pm was determined.

TiO2 is a very important thin film material in optics, because the refractive index is high, and also it can satisfy the requirements of a hard, dense and chemically stable coating. In our study, the effect of the floating potential, and the resulting ion beam bombardment on the properties of TiO2 thin film deposited by reactive planar magnetron sputtering has been observed. The dense plasma of an unbalanced planar magnetron was 'leaked' onto the substrate, and controlled by permanent magnets placed behind the substrate. This allowed the floating potential to be varied from -3 up to -59V. During sputtering, this bombardment was used as a neutralised ion beam to enhance film growth. To stabilise the oxygen partial pressure, an optical emission controller was used. It gave a complete range of Ti to oxygen ratios. As a result, we obtained samples with a maximum refractive index at 633nm of 2.52 and a deposition rate of about 4X/s. The properties measured were the refractive index, the surface composition and morphology, and the crystallinity. The relationship between the refractive index and the proportions of 'anatase' and 'rutile' crystal structures of the TiO2 film was especially considered. The highest floating potential showed up to 75% 'rutile' contents.

Titanium dioxide is extensively used as the high index film material in multilayer optical thin film devices. Optical absorption in the films depends upon deposition parameters, important among them being substrate temperature and starting material. In this investigation, single layer titanium dioxide films have been prepared by reactive electron beam evaporation of TiO in neutral and ionized oxygen medium. The substrate temperature is maintained in the range 25°C to 250°C and its influence on the optical absorption of the films is studied. The influence of film thickness on optical. absorption is also investigated. Films of thicknesses 1400 Å and 2800 Å have been deposited. With increasing substrate temperature, the absorption in TiO2 films deposited in neutral oxygen atmosphere increased and showed a maximum at 175°C for thinner films (1400Å) and 150°C for thicker films (2800Å). Though similar behaviour was observed in films deposited using ionized oxygen, the substrate temperature has been found to have only a marginal effect on optical absorption of these films. The variation in optical absorption in TiO2, films has been explained on the basis of variation in condensation of oxygen as well as the evaporant due to substrate heating.

Critical environmental conditions require optical components with enhanced surface characteristics in respect of mechanical and chemical damage. To this purpose, protective films that improve substrate cl-ia.:acte,-fistics without detriment of optical properties are used. In this paper a comparison between he properties of Y 0 and a-C:H as protective coatings in the 8-12 um is reported. The Y 0 films have been deposited by r.f. Sputtering and a-C:H by Dual ION Beam Sputtering on glass and germanium substrate. The measurements of refractive index and extinction coefficient of these films in the infrared wavelength range are presented. Moreover, the ultra-microhardness and adhesion of deposited films are compared.

A magnetron arc evaporation ion plating(MAEIP) system has been constructed using disk titanium cathode Ti-N thin film with gold-like colour has been prepared using MAEIP techniques. The reflectances of Ti-N thin films in the wavelength range 350-2500 nm has been measured at near normal incidence by UV-365 spectrophotometer. X-ray diffraction analysis shows that the magnetron arc evaporation ion plated Ti-N thin films are polycrystalline TiN. The TiN thin films as decorative and hard coatings have been widely used in the watch-covers, watch-chains, Badding iron balls and tools, etc.

Examples of microanalytical investigations show, that differences in the chemical and physical interactions between the substrates and adjacent material can occur, which can induce structural and compositional changes of the surface and whithin subsurface layers during the pretreatment of the substrates before coating. In particular, pretreatment can influence the properties and the optical properties of the optical surfaces on glass. Moreover, the deposition techniques also contribute to changes of the properties at the same time. Microanalysis can reveal chemical reactions also, by which different crystal-line or non-crystalline interfacial and subsurface layers are formed during processing at elevated temperatures, and which produce different surface properties depending on the processing parameters. This can be exemplified when analytical electron microscopy is applied together with in-depth profiling in combination, which provide the large spatial resolution required for these investigations. The lateral resolution of the analytical electron microscopy allows studying the formation of defects with dimensions smaller than 1 pm. The comparison of the various microanalysis results with the respective product properties and their dependence on the fabrication parameters provides data for process control and for obtaining a high degree of reproducibility of optical properties, which otherwise cannot be obtained. Concepts must be developed because of economy selecting the most adequate analysis methods for obtaining the required data.

Electron microscopy, stylus-type surface profilometry, and Raman microprobe characteri-zation show distinct differences between thin films deposited by reactive evaporation and by reactive ion plating. Reactive evaporation yields thin films with the well-known columnar microstructure with appreciable surface roughness and other deficiencies. Low-voltage, high-current reactive ion plating deposition produces thin films which are smooth and dense. Cross-section electron micrographs of ion plated coatings reveal a densely packed poly-crystalline structure for Zr09, while TiO2 appears to form vitreous films. Molecular dynamics computer simulation of the film formation process is in good qualitative agreement with the experiments. The results suggest the expansion of the Movchan-Demchishin structure zone model with an additional Zone 4 for the vitreous phase, resulting from superthermal film formation conditions (thermal spiking).

A conceptual design for a no-moving-parts ellipsometer with a calibration procedure to remove effects of imperfect components and detector sensitivity differences is described. The device is particularly useful for infrared (IR) coating monitoring, where high deposition rates are used and where detectors may be polarization-sensitive. A calibration scheme that uses only linearly polarized beams and no retardation components has been devised.

An optical monitoring system for the in-situ reflectivity measurement on the actual moving substrates during e-beam thin film batch deposition is described. The reflectivity of one of the substrates mounted on the caroussel and moving in a planetary motion during the deposition is measured at 2 laser wavelengths (HeNe green and red) and compared with computed curves to determine the end-points. Examples of deposited TiO2 films and a multi-layer dielectric mirror are given.

TO improve tne yiela or proauction or aielectric multilayer coatings an on-line correction method has been developed. Termination of the deposition of each individual layer using monochromatic optical monitoring, has been made adaptable to variations in the process. It is based on a method of on-line refractive index measurement. During deposition of the layer the required thickness is recalculated for the actual refractive index and the setting of the shutter is adjusted accordingly. The method allows to determine the index of single layers as well as more complex layer systems with arbitrary thicknesses. Combinations of test slides, or change of test slide after each layer, are possible. After deposition of each layer a process computer receives updated data for the type of material. Data for the next run are updated too. This paper gives an example of a multilayer anti-reflection coating generated by this process. Recorded process data are compared with data from inverse analyses of the spectral results. Coating results obtained with this method are compared with those of non-corrected runs.

We will describe the concept and operation principle of the newly developed monochromatic process photometer OMS 3000 for optical coating systems. It is designed as a true double beam instrument, completely controlled by modern microprocessor techniques. It offers high signal resolution and excellent long-term stability. The deposition of complicated layer systems is supported by an advanced monitoring software which precalculates the cut-off conditions. In addition, spectral measurements between layers are possible allowing the on-line-optimization via an external host computer.

For a long time, the use of very large mirror was devoted to astronomy observations. Due to the dimensions, the coating of such mirrors was a difficult challenge, but the precision on the value of the reflectance and the uniformity of the coating thickness were not very critical. Now, such mirrors are designed for other applications and their specifications are at the moment very hard to achieve.

The theoretical design of a high efficiency antireflection coating on germanium for the 8 to 11.5 micrometer band is a relatively simple matter, but the reduction to practice of a high durability version of such a coating is not as easy. The first requirement is to reduce the reflection losses due to the very high index of refraction without adding significant absorptance or scattering. The second is to provide resistance to the environmental conditions which might be encountered by the product. The practical problems of stress and adhesion, hardness and abrasion resistance, and salt fog and humidity resistance pose some major challenges to the transformation from a design to a successful coating process. We describe some of our experiences with the evolution of the process from theory to practice, some of the problems encountered, and what we believe we have learned. Due to the extensive number of variables and the constraint on time and resources, the development could not be totally rigorous or exhaustive. The judgement and experience of the development staff was exercised to focus the resources on areas which were perceived to offer the best possibility of a solution to the requirements. The net result of the work described here was a process with considerably improved properties over the starting point of the development.

By means of an optical in-situ stress monitor the intrinsic mechanical stresses in at various working gas pressures dc magnetron sputtered Al films were measured. At 0.1 Pa argon pressure the Al films showed compressive stresses, which decreased as the pressure was increased. The chemical composition of the films was investigated by AES and electron-beam microprobe. The content of oxygen and carbon was highest at high working gas pressures and low deposition rates. The argon content of all films was to small to be detected by microprobe analysis.

There are a number of systems known for the colour splitting of light used in television systems. One of the frequently beam splitting system used is the Philips prism system which has been implemented with many modifications. The Philips prism system consists of two prisms and an optical wedge with nonstandard angles. The Philips system also contains two thin film stacks which are not easy to manufacture in mass production. Further, great attention must be paid to the positioning of the components during their assembly. The new beam splitting system being developed in our laboratory is to be used in cameras for robotic systems, TV or video cameras containing tubes or COD chips. The major advantages of the new system over the Philips prism are a) almost complete insensitivity to the polarization of the incident light, b) better colour balance over the whole aperture and, c) a lower weight. The new prism system offer the following advantages: a) it is assembled from standard optical parts, namely right angle prisms, b) it is easy to compensate the optical paths of three independent colour channels by the adding of two planoparallel plates to the two channels, c) there is possibility to maintain the fourth white or infrared channel very easy to fulfil colorimetry criterion of television systems. There is still one optical thin film stack which is difficult to implement, but that is one less than in the Philips prism. The main difference between the new prism and the Philips prism is that the new beam-combiner contains anisotropic optical component. This paper describes the principal scheme, the results of mathematical models generating the chromatic characteristics and, the design of partially polarizing stack with the thin film technology used.

Highest quality dielectric films are required today for various interference optical applications and for planar wave guides in integrated optics. Many inorganic chemical compounds which were difficult to deposit by conventional techniques in form of well adherent, dense, hard and stable low-loss films are now routinly synthesized by reactive gas discharge plasma and energetic ion and/or coating materials atom processes. A survey over such PVD coating technologies and on the resulting film properties is given in this paper.

New magnetic materials and X Ray mirrors lead to prepare multilayered structures (M.L.S.) with the thinnest periodic layers. However physical limitations appear for periods below some tens of Å. In particular, tolerances of realization are critical relatively to ultrathin thicknesses values. In sputtering, the deposition rate is easily reproducible, and can be maintained at a constant and low value during severals hours; for these reasons we are able to perform a large number (more than one hundred) of periodic ultrathin layers by this system (3 to 1.5 nm). High Resolution Transmission Electron Microscopy (H.R.T.E.M.) and X Ray reflectivity measurements are used to compare interfaces and stacking regularities for sample with 140 layers. The W/Si M.L.S. present a best quality, as for interfaces and structures, compared to the W/C M.L.S.

For the wavelength region from 24A to 44A, selection of materials used for the multi-layer mirror was done by computer simulation. The multilayers of Si02/Ni were produced by the ion beam sputtering method and evaluated by the C-K line, experimentally. In order to analyze scattering in the region of 0 ~ λ comparisons between the experimental results, and the solutions of Beckmann's theory and Extinction theory were done.

High reflectance low-scatter mirrors have been developed for laser-gyro applications. Different types of multilayer systems: Ti02/Si02, Ag/Ti02/Si02, and Ta205/Si02 combinations were investigated. In the first system TiO2 was rf-sputtered while Si02 was electron-gun evaporated. The best results were achieved for these materials with 21 alternating λ /4 layers. In the second system a thin silver film was rf-sputtered as a first layer on the substrate. Ten additional dielectric layers on the silver base were deposited to reach the same reflectivity as with pure dielectric mirrors. In the third system both Ta205 and Si02 were electron-gun evaporated. The best quality was achieved with 29 alternating layers. The mirrors of Ti02/Si02 and Ag/Ti02/Si02 exhibited no shift of the center wave length after exposition to air, while the mirrors of Ta205 /Si02 showed a shift of 30 nm. The mirrors were investigated in terms of reflectivity and scattering using an ultraprecise measurement equipment. Scattering was measured in an Ulbricht integrating sphere; resolution: 0.2-10-6 . Reflectivity measurements were carried out in a special developed reflectometer; resolution: 10.10-6.

An important requirement for the operation of ring laser gyroscopes is the uncoupling of counter propagating modes inside the resonator. We report on the development of a resonator mirror with magneto-optic features that should permit lock-in suppression by exploiting the non-reciprocity of the transverse magnetic Kerr effect. This effect manifests as a non reciprocal phase shift of p-polarized waves reflected by such a mirror, thus causing unequal optical path lengths of the counter propagating modes and inducing a frequency split which lifts the unwanted coupling. A Bi-substituted yttrium iron garnet layer is the carrier of the magneto optic properties which have been induced by post deposition heat treatment. This causes recrystallization of the film which, as deposited by RF sputtering, is in amorphous phase. Garnet films producing a sufficiently pronounced magneto optic effect could be obtained with annealing temperatures as low as 550° C. Films of this type have then been applied to a dielectric multilayer stack which served as highly reflecting base. Absorption of the garnet films necessitates a trade-off between loss and magneto optic performance of the mirrors. Mirrors for λ= 633 nm and 30° and 45° angle of incidence have been produced after establishing the optimum design.

Ta205/Si02, Zr02/SiO2 and TiO2/SiO2 multilayer optical interference filters were deposited in a Balzers2BAP 800 coatiftg plant by reactive low-voltage ion plating. The spectral filter characteristics were investigated with respect to time and temperature. The observed stability is correlated to the water and hydrogen contents. The temperature derivatives of the refractive index of TiO2, ZrO2 and Ta205 were estimated.

The transmission of interference filters consisting of Ta205, Ti02, Zr02 and Si02 layers were measured at temperatures between 25°C and 185°C. Some characteristic differences between filters produced by reactive evaporation and reactive ion plating are demonstrated and discussed.

Molecular Beam and Ultra-High Vacuum techniques have been applied to the deposition of optical thin films and structures. Materials studied include ZnSe, ZnS, BaF2 and PbF2. Properties of microstructure and crystallite size have been studied using cross sectional TEM techniques. MBE techniques enable the production of novel thin film structures such as Bragg reflectors and graded index anti-reflection coatings. Etalon filters fabricated using this method show consierably improved long term operating stability over those produced by conventional evaporation.

Thin film GaAs layers grown by Molecular Beam Epitaxy (MBE) on silicon, semi-insulating GaAs, and insulating substrates have been investigated for application to optoelectronic circuit technology. Photoconductivity measurements were conducted to characterize the electronic transport properties of the epitaxial layers in terms of carrier recombination lifetime and effective drift mobility. By varying the epitaxial growth parameters, it is possible to obtain various levels of material quality which are suitable for various components of optoelectronic integrated circuits. Results from photodetectors fabricated from GaAs grown on various layers will be presented. The fabrication of ridge waveguides from GaAs grown on silicon dioxide will also be described. Finally, a procedure for growing high quality GaAs for active devices in situ with layers for picosecond photoconductors will be discussed.

The possibility of generating optical thin-film structures with continuous variation in refractive index enables the design and fabrication of complex filter structures. New methods for coating design, deposition monitoring, process control and material engineering are evolving. A particular type of filter technology that draws on all of these developments is the rugate filter, a structure having a periodic re-fractive index profile. Advances in this area will not only enable the realization of gradient-index structures, but will provide new opportunities for accurate fabrication of conventional thin-film structures.

A method for designing thin-film optical filters based on simulated annealing techniques is outlined. In contrast to conventional methods, it does not require the user to provide a starting design and it is able to find good solutions separated by barriers in the quality function. To illustrate and discuss some of its main features, two types of design examples are presented: (i) a green/cyan colorimetric filter for use in television cameras, where cyan results from removal of the top part of the green stack, and (ii) a two peak filter for transmitting the red and green HeNe laser lines simultaneously.

Bombardment of growing films with reactive particles has developed into a powerful technology over the last 3o years. Compared to normal evaporation methods, important improvements are: better adhesion between film and substrate, high film density, fast coating rate and stoichiometric layers with low optical losses. Although the techniques used to achieve the desired properties vary quite dramatically from high pressure plasma processing to bombardment with monoenergetic ion beams in ultra high vacuum environment, from particles with nearly thermal to some keV energy and from discharge currents of some μA to more than 1oo A in industrial applications, the ion-surface interaction, which causes the modification of the films, is the basic of all reactive deposition processes. The purpose of this paper is to review plasma processes for the production of optical coatings including ion assisted deposition, ion plating and ion cluster beam deposition, comparing the structural and optical properties of the films. Some applications of reactive evaporation presented in the following papers demonstrate the potential use of reactive evaporation and plasma processes for solving optical problems.

Light guiding and modulation was demonstrated in sputtered LiNbO3 films deposited on glass substrates. The films exhibit exceptionally low attenuation (< 2dB/cm) and the highest electrooptical coefficient reported so far for this kind of films (1.34 x 10-12 m/V).