This paper samples the current open literature in order to delineate trends in advanced optical materials. Recent symposia on this general subject have been sponsored by the Society of Photo-optical and Instrumentation Engineers (1981, 1982, and the current 1983 meeting) and an analysis of these papers has been made along with other related publications. Significant development is evident in ultraviolet and infrared transmitting materials, laser windows, special glasses, glasses for fiber optics, improved resistance of optical materials to a variety of stressful environments, and improved optical blacks. Interest in scattering and reduction of scattering in bulk optical materials and from surfaces continues to be a subject of research. Improved instruments for measuring scattering are in development. Additional current optical materials technology thrusts are described.

The alkaline earth-rare earth sulphide family has been identified as an interesting new class of materials with potential for application as broad band infra-red windows. These sulphides are generally refractory and show potential for exhibiting better thermal and mechanical properties than the binary zinc chalcogenides, zinc sulphide and zinc selenide, both currently available broad band window materials at an advanced stage of development. Within this ternary rare earth sulphide family attention has been focussed on compounds with the cubic thorium phosphide structure, and in particular upon calcium lanthanum sulphide, CaLa2S4. This paper describes the preparation of CaLa2S4 ceramics from ternary sulphide powders using a variety of densification techniques and also reports the results of some initial property determinations.

Currently available materials such as ZnS or ZnSe which have excellent optical properties in the 8-12 μm spectral band have been shown to be susceptible to rain impact damage. In recent years interest has been shown in a family of rare earth ternary compounds which offer the potential of improved thermal and mechanical properties while retaining similar transmission characteristics to ZnS and ZnSe. An examination has been carried out of the densification of SrLa2S4, CaLa2S4, MgSc2S4, CdEr2S4 and La2S3 using a hot pressing technique. The phase composition of the products has been studied using X-ray diffraction and Raman spectroscopy whilst the optical properties have been assessed by transmission spectrophotometry. The measured hardnesses of these rare earth sulphides are significantly in excess of those of other wide-band gap optical materials such as ZnS and ZnSe, although the values of coefficients of expansion are greater. The full value of these new emerging materials cannot be determined until improved material has been fabricated for measurement of other properties such as rupture modulus, Young's modulus and thermal conductivity. But the potential improvement offered by these materials in comparison to impurity hardened ZnS and ZnSe is discussed on the basis of currently available data.

Keeping in view the importance of the development of antireflection coatings (ARC) on germanium (Ge) and silicon (Si) in the infrared region, suitable for terrestrial and space applications, the optical, thermal and mechanical properties of various semiconducting and dielectric materials are briefly reviewed. Cadmium telluride (CdTe) and zinc selenide (ZnSe) which are found to be the most suitable materials for ARC systems are deposited on Ge and their optical and non-optical properties are studied in detail. It is found that both these coatings enhance the transmission of Ge by 100%. CdTe coatings in particular are found to withstand all severe environmental tests as per military specifications.

High transparency in the ultra-violet, visible and infrared spectral regions can be achieved in polycrystalline MgAl204 by using high purity starting materials and advanced hot-pressing technology. Optical and mechanical property data at room and elevated temperatures will be reviewed. Shape and size limitations will be discussed. Prices will be projected.

Controlled crystallization of a glass of the As-Ge-Se system, nucleated by hafnium resulted in production of glass-ceramics with better thermomechanical properties than the starting glass while conserving good IR transmission in the 7-12μm range. This range is extended to 15μm by the addition of hafnium . The mechanism, of devitrification is investigated as well as the evolution of IR transmission with temperature.

Design and technology of modern optical systems in the visible part of the spectrum demand for more and more sophisticated glasses with regard to special properties. Athermal behavior of optical data, extreme low fluorescence and scattering, the stabilization against any kind of radiation and high transmission and chemical stability against the different aggressive media are some of the topics of interest beside the basic information of refractive index, its dependence on wavelength and relative partial dispersion. The current status of these demands, some thought about basic limitations and their future aspects of improving these properties are discussed.

Heavy metal fluoride glasses offer considerable potential interest for a wide variety of applications in visible and mid I.R., such as optical waveguides, I.R. domes, windows, laser hosts, etc... ZrF4 based glasses with a transmission in the 0,2 - 7 μm band, and ThF4-ZnF2 based glasses with an I.R. absorption edge in the 8-9 μm region, are potential ultratransparent materials for the 3-5 μm window. The main characteristics of these two classes of vitreous materials are detailed here, including preparation, manufacturing, optical and thermal properties.

Zirconium fluoride glasses are the best known and the most stable beryllium-free glasses. They offer numerous potential uses for I.R.-transmitting fibres and ultra-long repeaterless optical wave-guides. Various problems arise in the manufacturing of fluoride glass fibres, essentially because of the steep viscosity profile and the devitrification phenomena. This paper discusses the processes for manufacturing step-index preforms and for drawing fibres. Optical quality preforms have been obtained and fibres have been drawn over more than 1 km. A spectral loss measurement system has been constructed using fluoride glass optical components. Several curves showing the optical attenuation versus wavelength are presented and discussed. These fibres are now available for optical transmission in infra-red systems.

A review is given of the development of laser glass. The fluorescence and laser effect of numerous glass compositions has been investigated in the last twenty years. But the industrial application is small in comparison to the research volume: between 20 and 30 glass types are available commercially today. Phosphate glasses are in the foreground nowadays, because they have a high laser effect and it is possible to produce them in large volumes and with high damage threshold. They are used for high power lasers and lasers for materials working and measuring technique.

The ternary glass forming system Se-Ge-As, typical for chalcogenide systems, was chosen for consideration. Preparation of glasses and their homogeneities and structures are discussed. Properties like density, Tg values, elastic constants, strength, self diffusion, gas solubility and chemical stability are reported. The non-linear relationship between properties and composition is explained structurally.

In the field of optical high precision elements, which have to be extremly stable in form and dimensions during variations of temperature, mechanical forces and time glass-ceramics reckoned among the best in the family of zero expansion materials.

Ion implantation and ion mixing have made possible the production of new materials having new properties and new phases or structures. Typically, the optical properties modification of material by implantation strongly depends on the chemical bonding in the matrix. In the particular case of insulators these modifications can result in two different ways : the creation of intrinsic defects associated with energy loss processes (electronic excitations or nuclear collisions) and extrinsic defects due to the doping. The defect concentration is inhomogeneous in depth as the energy loss profiles which is very usefull for waveguide applications to obtain a refractive index gradient or a coloration gradient. The implantation of chemically reactive ions in materials is a non conventionnal way of doping. Bonding and charge transfert effects can induce strong modifications of the optical properties of the implanted layer. In addition for heavily implanted materials, new phases can be formed by precipitation processes such as small metallic clusters embedded in an insulator. Their implications in solar energy conversion are important for selective absorber production.

Integrated optic devices are normally confined to within a few microns of the surface. This is the depth scale which is readily accessible to ion implantation techniques. Optical waveguides and associated components may thus be written directly into a substrate or thin film by a combination of masking and ion implantation. The earlier development of implantation for semiconductors has been extremely successful and liberated circuit design from the constraints of diffusion controlled circuits and allowed high tolerance, high density integrated circuits to be formed. For optical systems similar advantages allow refractive index depth profiling, strong lateral confinement of low loss waveguides and spatial variation of electro-optic and SAW properties. A full exploitation of the implantation techniques to thin film systems has still to be made. This paper will give examples of current progress in ion implanted waveguides and electro-optic devices with materials ranging from silica and lithium niobate to gallium arsenide. These will demonstrate the mechanisms by which the refractive index or optical properties can be controlled. Related ion implantation effects will be briefly mentioned.

In this paper a systematic investigation on the optical behaviour of 40-100 keV Ar implant ed alkali glasses will be discussed. The implantation of soda-lime glasses resulted in a surface layer formation which presents a decreased refractive index. The thickness and average refractive index of such layer have been evaluated from the position and height of the interferential minima, observed in the reflectance curves. The significative antireflective improvement of the implanted glass has been connected to a surface alkali depletion, due to a preferential sputtering and an enhanced diffusion over the implanted ion range.

A new way of producing selective solar absorbing surfaces using ionic irradiation is described. The different techniques of ion beam production of metal-insulator composites are developed using a model system (alkali metals-LiF) and first results are presented on a gold-MgO mixture, which constitutes a very promising system for solar energy conversion in the high energy range. Complementary techniques of characterization using Rutherford Backscattering Spectroscopy and Optical Absorption are described. First results on the formation of Au-MgO composites by ion beam mixing are in particular discussed.

Two special methods were developed to produce antireflective - interference - layer-systems. One is the dip coating process - an additive method. The other method is the neutral solution process - a substractive method. The antireflective layers from both processes are well suited for high power laser systems. A method is described to measure a refractive index gradient in thin layers - as for example leached layers.

The solar selective properties of the copper oxides Cu20 and CuO on stainless steel have been studied. Copper oxide/stainless steel tandems have been prepared by thermal oxidation of sputtered copper films on sputtered steel films. The reflectance spectra for this type of tandem absorber show excellent agreement with calculated spectra. The calculations were performed with conventional optical interference formalism using the optical constants for the free oxides and polished stainless steel as input. For comparison copper films were also deposited by electrolysis from a copper sulphate solution. This preparation technique supresses the reflectance in the visible, which increases the solar absorption. It is suggested that the CuO/SS-tandem suffers less from thermal degradation than the CuO/Cu-tandem.

In recent years amorphous carbon coatings found growing interest because of their optical and protective properties. We have deposited hydrogenated amorphous carbon films (a-C:H) from an RF excited discharge in benzene vapour. Substrates include germanium, glass and MgF2. The refractive index can be tuned between 1.8 and 2.2 and efficient antireflection coatings on Ge have been prepared. We have determined the optical absorption from the UV to the IR range (0.2 - 25 μm). A typical 1 µm thick a-C:H film is transparent (> 50% transmission) from 750 nm to the far infrared. Amorphous carbon films are harder than sapphire and are resistant to concentrated acids and bases.

The Martin Black process has been used to coat baffles on a wide variety of visible and ultraviolet range instruments. Its infrared applications include baffles for the Infrared Astronomy Satellite and the Spacelab 2 Infrared Telescope. Because of the increased emphasis on stray light suppression in the infrared, a series of experiments on the Martin Black process were conducted with the objective of better understanding the effects of various processing parameters on obtaining a blacker infrared surface. These experiments resulted in the creation of an infrared absorbing surface, called Infrablack, which retains the excellent visible absorption properties of its predecessor and has increased infrared absorption. We report here measurements made on the new surface that characterize its optical properties in the infrared. These measurements represent the results of only the first stage of our improvement program. Data are presented on the specular and hemispherical reflectivity and the BRDF (Bidirectional Reflectance Distribution Function) of the Infrablack. The measurements to date support the belief that the Infrablack surface can be made even more absorbent in the infrared in the next phase of the process improve-ment.

A number of interesting materials that exhibit "active" optical properties such as electrooptics, non linearity, etc., cannot be used in integrated optics because of the lack of a versatile technique for making waveguide out of them. We discuss and illustrate such a technique which makes use of passive layers deposited on the active substrates. Second harmonic generation in a structure composed of a quartz crystal as a substrate and hydrogenated amorphous silicon as a passive layer is demonstrated.

The optimum combination of wavelenghts required for achromatism to minimize the residual spectrum of lens systems is only known for the wavelength range between 0.365 and 1.014 μm. For this reason a procedure is discussed which permits the calculation of zero-thickness lens systems whose sum of the squared chromatic longitudinal deviations is a minimum in the spectral range of interest. As a guide to proper materials development the investigations also covered materials whose mechanical or climatic resistance is unsatisfactory.

Vanadium dioxide (V02) film exhibits semiconductor-to-metal transition at temperature, Tt near 340 K. The transition is accompanied by changes in optical transmission and relection. In this paper the reflected light spectra were experimentally determined at the two temperatures below and above Tt (300 and 360 K) using film thickness as the parameter. Then we calculated the ratio, Kλ , of reflection coefficient, Rm, in metallic phase to reflection coefficient, Rsc, in semiconductor phase. The film for which the maximum Kλ was observed at λ =1.06μm applied as a mirror in Nd:glass laser. The laser generated giant pulse with duration time at about 50 ns.

The BSO crystal must be described as an elliptical birefringent. Under the photo-induced modulation of an applied electric-field, the analysis of its polarization effect can be usefully splitted into successive operators, defined as a rotatory power followed with a linear birefringence, providing that proper values are determined for these equivalent operators, which are not identical to the intrinsic optical activity and birefringence of the crystal. A theoretical analysis of this elliptical birefringence is presented, together with experimental results. One shows that the definition of the half-wave voltage, usually considered as a characteristic, does not apply correctly to optically active crystals. Correction terms are calculated and a new method is also implemented, to determine the electro-optic coefficient. The results are given for the BSO crystal in the full visible range. These results are shown to allow a computer simulation of the performances, which enables to choose the optimal geometry of the crystal for any specific application.

The current state of the art in selected coatings for plastic optical elements (PMMA, polycarbonate, CR 39) is discussed. Experience gained in the development work, which led to production-proven coatings on optical elements to be used in transmission in the visible range, demonstrates that the substrate quality determines the quality of the final coated element to a large degree and thus partly also the extent to which coated optical plastic is able to replace mineral glass. Consequently, the requirements which have to be met by current and future plastic substrate materials are listed in detail.

The electrochromic properties of thin films prepared by electropolymerization of pyrrole and 2,2' bithiophene are described. The films change color reversibly when they are electrochemically cycled. The response times are less than 150 ms and the stability under repetitive cycling is good (105 cycles). The electrochromic parameters are compared to those of other electrochromic polymers.

Transparent single crystals of different phenols are grown from the melt or from saturated solution in various solvents. Crystal structure determination are studied by X-Ray or neutron diffraction methods. Among them several are used to measure physical properties. For this paper we choose non linear optical properties. Measurements first made on powder to know the importance of the phenomena have to be repeated on single crystals in several directions to know coefficients of the NLO tensor. At present time data are known for 3-methyl-4-isopropylphenol (tetragonal - space group P41). These negative uniaxial crystals are found to have NLO coefficients (d333, d331) = (1.1, 1.4) x 10-9 esu respectively. On the other hand, data show that nx at 0.53 μ is almost equal to nz at 1.06 μ (Δn = 0.0023). This fact means that the coherence length for the second harmonic generation at 1.06 μ is very large. If in fact the two indices were identically equal, we would have a very useful crystal as a device for doubling the readily available 1.06 μ source up to 0.53 μ, particularly since there are only few crystals known which have this quality. Same measurements have to be made on an isomorphous compound, 4-isopropylphenol. The two compounds syncrystallizes to give solid solution ; so it will be interesting to grow, if possible, single crystals of intermediate composition and made NLO measurements on them.

New nitrobenzene and nitropyridine derivatives have been designed and studied in powder form. Second harmonic generation (SHG) efficiencies range between 25 and 160 times that of urea. They are all transparent for wavelengths greater than 0.5 μm and one of them, MBA-NP has been proved to be non critically phase matchable at 0.9 μm.