Optical glasses are fine annealed with annealing rates of about 7 to less than 1 K/hour in order to reduce residual stresses and to avoid inhomogeneities induced by the stress in the glass, such as birefringence and small variations of the density and the refractive index. Upon annealing in a temperature range from the glass transition temperature Tg to Tg-150 K the properties of optical glasses are often assumed to be essentially independent on the subsequent annealing procedure at temperatures below that range. In contrast to this expectation, however, it has been observed that the refractive index can be changed by heat treatment pro-cedures far below that range. These effects of heat treatment can occur during cementing, polishing and coating of optical components made from these glasses. In a recent study, samples of different types of optical glasses have been heated to tempera-tures 100 K, 200 K or as low as 300 K below Tg and subsequently these samples have been coarse or fast annealed to room tem-perature. Depending on the type of glass we have observed changes of the refractive index even as large as some 10-4 with respect to its former value. An overview will be given on the behaviour of those different types of glass investigated until now.

Infrared reflectance spectra of silica glass implanted with Ti, Cr, Mn, Fe, and Bi to doses between 0.5 - 6 x 1016 cm-2 have been measured from 5000 cm-1 to 400 cm-1 at room temperature. The ion energy of the implantation was 160 KeV and the current was 10μA. Alterations in reflectance of bands at 1125 and 481 cm-1 in the spectrum of an unimplanted sample of the order of 20% are observed. A band attributed to non-bridging oxygen ions at -1015 cm-1 is observed to increase in intensity with increasing dose for all species. The band at 1125 cm-1 is observed to shift to lower wavenumber with implantation. Bands due to implanted ion-oxygen vibrations were not detected. The magnitudes of the effects on the existing bands were ion specific. This ion specificity is attributed to the differing chemical states of the implanted ions after implantation.

When choosing optimum materials for system components, the optical designer must consider many material characteristics. Optical parameters as well as structural and environmental requirements must be specified and toleranced. System performance and operating and storage requirements must be generated first to ensure that the optics contribute their required functional share. For example, whether or not focus of an objective or beam divergence of an afocal can be passively maintained by athermalization or by servo-driven feedback can largely depend on the selection of optical materials and their mechanical mountings. Laser damage thresholds may require inclusion-free materials and low scattering surfaces. These sur-faces can be another driver of substrate selection. Continued efforts in uniformly and more completely specifying optical materials are required to achieve a more predictable level of excellence in performance of EO systems. This paper provides both an overview of optical materials and application-oriented considerations for their selection.

This paper describes a preliminary study of the refractive index dispersion in the beryllium fluoride (BeF2) melted glasses doped with aluminum fluoride (A1F3). It is shown that these glasses have very low dispersion, an order of magnitude lower than silica glass. It is further shown that doping BeF2 with A1F3 increases the refractive index of the base glass. Thus, an optical waveguide fiber design with BeF2 as the cladding and A1F3 doped BeF2 as the core is feasible. Also, the index dispersion of a melted BeF2 glass is compared with that of a CVD (chemical vapor deposition) glass. In the past it has been shown that fluoride glasses possess excellent transparency from the near UV to mid IR. The most interesting properties of fluoride glasses are that they possess low refractive index, low dispersion and low Rayleigh scattering. Hence, the potential for making an ultra low loss, ultra long optical fiber exists. The major intrinsic losses in a pure fluoride glass fiber would be the Rayleigh scattering which is proportional to the inverse fourth power of wavelength. Intrinsic attenuation losses of 0.001 dB/km are possible in high-purity fibers in the 2 to 4 gm wavelength range. Major efforts in fluoride glass technology have focused on fiber fabrication with zirconium tetrafluoride-based glasses, melted conventionally. Such systems can contain from two to five components. An alternate approach is the CVD of fluoride glass systems being developed at Corning. An organo-metallic compound has been processed to fabricate BeF2 glass. The ZrF4 -based glasses do not lend themselves to CVD processes because of the problems in finding suitable precursors with the required vapor pressures.

Transparent and colorless glass rods have been obtained from the A1F3-ZrF4-YF3-CaF2-SrF2-BaF2-NaF (AZYCSBN) and A1F3-BaF2- CaF2-YF3-SrF2 (ABCYS) systems. Chemical durability and certain optical properties of these glasses have been investigated and compared with ZBLAN. The infrared transparency of AZYCSBN is slightly less than ZBLAN but higher than the ABCYS glass system. A1F3 based glasses appear to offer some interesting opportunities for short range IR fiber applications such as sensing, remote spectroscopy and laser power propagation.

Elastic hysteresis phenomena were observed in ULE and Zerodur glasses at elevated temperatures up to glass transition. These effects were found under load deformation testing using four-point bending. Permanent creep resulted in Zerodur at 900°C and in ULE at 1000°C. The deformation was monitored at mid-span of the samples with a capacitance-type transducer having 0.01 micrometer resolution. These hysteresis.effects may be classified as elastic bimodulus between loading and unloading; that is, two different elastic moduli were observed between loading and unloading. Upon complete unloading, a minimal deformation state promptly returned, indicating little or no viscoelastic creep. The hysteresis effect may be attributed to a change in glass structure as a function of stress state. A description of the test apparatus and procedure, test results for both glasses at several elevated temperatures, and an elementary discussion of continuum theory of constitutive behavior are included.

The optical anisotropy properties of glass samples can be well determined by four measurands: relative retardation A, orientation of the optical fast axis 9, polarization-dependent loss angle 4', and pseudoactivity angle p. Using our transmission ellipsometric method, it is possible to ascertain these four characteristic quantities with high resolution and their dependence on the beam position in the sample. In relation to polarization microscopes which are often applied in quality control to analyze anisotropies, this new ellipsometric method is slower but more sensitive by a factor of 1000. Especially glass samples or optical components with plane parallel surfaces are suitable for high accuracy measurements applying the transmission ellipsometric method. For perpendicular incidence of the laser beam of the ellipsometer, the material-dependent anisotropies in the coated or uncoated sample dominate and can be precisely determined if the disturbing Fabry-Perot-resonance response of the sample is known or avoided. The influence of the sample surfaces on the measured anisotropy can be estimated by an equivalent optical circuit diagram. The performance of the transmission ellipsometric method developed by us is demonstrated by measurements of different glass samples.

Ellipsometric parameters v and A for glass samples were measured at multiple angles of incidence using an infrared ellipsometer in the null mode. The Fresnel equations were fit to the data using a least-square-fit program to minimize both random and systematic errors in the measurements of the complex optical constants. A fused silica sample with roughness of 0.5 nm rms was used to test the system. The deviations of v and A from theory are at the level of the instrumental errors. The deviations from theory in n and k are less than 0.001 and the best-fit n and k determined for the sample at different wavelengths agree to this accuracy with Handbook values. We conclude that careful ellipsometric characterization can give indices of refraction to three decimal places for materials with low k.

Materials for large space optics require low coefficients of thermal expansion (CTE) in order for the components fabricated from them to maintain their strict figure specifications under thermal gradients and cycling. The environment in space contains high energy photons and charged particles such as electrons and protons, which can cause electronic defects, leading to such physical effects as compaction and discoloration. The change in CTE upon exposure to ionizing radiation has been studied here, and it has been found that the low-CTE characteristics of some materials are severely effected by electron irradiation.

The Moller-Wedel Goniometer-Spectrometer Model 1 is a high accuracy instrument for the determination of prism angles and index of refraction in the visible wavelength range (400-700nm). The instrument is capable of absolute accuracy to ± 0.2 arcsec for prism angle measurements, and ±1X10-6 for index of refraction measurements. Recently, we have developed a modified version of this instrument to provide absolute index of refraction measurements in the Near Infrared (NIR) wavelength range (800-2400 nm). The absolute accuracy for index of refraction measurements in the NIR is ±1X10-6.

Gallium Arsenide thin films have been successfully grown onto (1102) sapphire substrates by Molecular Beam Epitaxy methods using a graded growth procedure. The initial layers of GaAs were grown at lower growth rates and at lower substrate temperatures, followed by a thicker GaAs layer grown at usual growth rate of 1 pm/h. The films grown at temperature of 585 °C show good surface morphology. Silicon doped GaAs films exhibit n type conductivity and show low temperature photoluminescence band with peak energy at 1.502 eV and line width of about 42 meV.

TiO2 and Al203 films were developed by laser chemical vapor deposition (LCVD) technique on silica and D-shaped Si02-Ge02 fiber surfaces. The films were produced by CO2 laser assisted dissociation of TiCI4, AlC13, and trimethyl aluminum and diffusion of ions in the glass. The laser power chosen was to be between 100 and 550 W and the exposure time ranged from 20 to 120 sec. The films were analyzed by SIMS, XPS, ellipsometry, and XRD. The T102 film thickness was varied between 1.5 and 3.5 pm thru the exposure time and laser power variation. XPS demonstrated the formation of TiO2 and A103 on glass surfaces while XRD indicated the growth of rutile on glasses with the 110-axis perpendicular to their surface. The refractive index of the glasses increased from 1.4588 up to 2.505 after TiO2 deposition.

The chalcohalide glasses which are mixtures of halides and chalcogenides have received very little attention. This paper reviews the structures and properties of the known chalcohalide glass forming systems. These glasses possess interesting optical properties which makes them candidates for potential applications in the mid-IR, especially the CO2 laser which operates at 10.6μm.

The contributions of individual impurities to the total absorption loss in phosphate laser glasses have been analyzed. In a previous study, small melts with intentional impurities were analyzed as a means of determining the absorption coefficients for specific impurities. Since that study, the conditions for melting of large castings of phosphate glass have been modified toward substantially higher oxygen fugacity so that microscopic platinum inclusions can be dissolved to prevent laser-induced damage. In this study, we present absorption coefficient measurements at the laser wavelength (1.05 pm) for most common transition metal impurities as well as platinum in phosphate laser glasses melted under the modern oxidizing conditions.

Two new families of gradient index glass are discussed with an emphasis on fabrication.

An RF heated, bottom drain furnace/crucible assembly capable of melting up to 1 liter (z4.3 kg) of fluorozirconate glass is described. The apparatus was used in conjunction with gas and oil cooled molds to prepare glass discs of the ZBLAN composition z13 cm in diameter with thicknesses of z1.2-2.5 cm. Mathematical modelling of the thermal conditions associated with the fabrication of large castings was also carried out. These calculations were used to examine the limits on casting thickness and develop engineering designs for molds capable of producing large crystal and crack-free discs.

The refractive index dispersion characteristics of CdF2-LiF-A1F3-PbF2 (CLAP) systems were measured by the minimum deviation method. The refractive index changes from 1.64 (at 0.3892 μm) to 1.54 (at 5.3036 μm). The material dispersion curve is relatively flat in the wavelength region from 1 μm to 3 μm. The zero material dispersion wavelength occurs near 1.9 μm)which is the longest value reported for the fluoride glasses. Postulating a step index single mode fiber and calculating a waveguide dispersion, the total dispersion was obtained for CLAP fibers. From the comparison of total dispersion curve for CLAP and a silica fiber, it is shown that the dispersion can be mutually compensated in the wavelength range from 1.32 μm to 2.0 μm.

This paper expands on the use of sol-gel derived materials as host for organic molecules which possess nonlinear optical properties. Polymethylmethacrylate (PMMA) modified Si02 is a type of organically modified silicate (ORMOSIL) in which the PMMA is chemically bonded to the SiO, network. The preparation and characterization of bulk samples of PMMA modified Si01 host material and thin films of the host material doped with either 2-methyl-4-nitroaniline (MNA) or Rhodamine 6G are described.

Glasses in Nd203 - Si02 system were prepared. The maximum neodymia incorporated into the glasses, without inducing phase separation, was 5 wt%. The glasses were also nitrided and the resulting optical properties / structure examined. It was found that increasing neodymia and nitrogen contents increase refractive index.

Fluorophosphate and fluoride glasses containing nitrogen were synthesized by using nitride additives such as A1N, Ba3N2, and ZrN. Optical transmission and refractive indices were measured. Ammonia gas treatment of fluorophosphate glass melts was also successful for producing nitrided samples.

Luminescence from high-purity synthetic silicas, Spectrosil, Spectrosil WF, Suprasil 1, and Suprasil W1 , has been monitored in situ by an optical detection system during 50 eV synchrotron photon exposure at room temperature in ultra-high vacuum. Three luminescence bands were found, centered approximately at 290, 450, and 650 nm. Samples were divided into two sets. One set was irradiated by 137Cs gamma rays and another set was virgin samples. Then all the samples were exposed under 50 eV light from a synchrotron source. Photons, 50 eV, stimulate more intense luminescence in pre-irradiated silicas than in virgin silicas. Increasing the exposure time to UV light on the same spot, initially irradiated, increases the luminescence intensity for both set of samples. After an exposure of 25 minutes, the intensities of the 290 and 650 nm bands increased by a factor <1 while the 450 nm band increased by a factor of three. Electron Paramagnetic Resonance spectroscopy was used to determine the correlation between the concentrations of paramagnetic centers, e.g. E' centers, intro-duced by gamma rays or UV light and the total dose of the 50 eV photons. We found that E' centers increase linearly with the increasing dose of 50 eV photons. The rate of increase of intensities of the luminescent bands decreased with increasing exposure. 290 and 650 nm bands increase slowly with increasing exposure, while intensity of 450 nm band increases three times with increase of exposure time from 5 to 25 minutes in Suprasil 1. These results show that defects created either by gamma-ray radiation or by UV light enhance dynamic luminescence processes in silica. We tentatively attribute the more intense luminescence in gamma-ray irradiated samples under 50 eV light exposure to E' centers introduced by the gamma-ray irradiation. The increase of luminescence intensity with exposure time to 50 eV light is also attributed to the introduction of the E' centers by 50 eV photons in silicas. Possible defect-enhanced luminescence mechanisms will be discussed through electron-hole interactions with defect states in the bandgap.

Defect centers induced by 6.4 eV laser light in high purity silica were studied by electron spin resonance (ESR). Both Si E' centers, and non-bridging oxygen hole centers (NBOHCs) were observed. However, the E' center was the dominant defect in type III synthetic silicas (1200 ppm OH), while the NBOHC was dominant in type IV silicas (< 5 ppm OH). Formyl radicals (HCO) and hydrogen-associated centers were also observed in high-water silica. The concentrations of both Si E' centers and NBOHCs were found to increase as the square of the 6.4 eV laser power suggesting that they are induced through non-linear absorption of UV light. By contrast, we find that the HCO concentration increases linearly at low laser power, saturates, and decreases at high power. Excitons induced by the non-linear absorption of UV light are inferred to be responsible for the generation of these observed defect centers in high purity silica.

Fluor crown glasses, having improved transparency in the UV-spectral region, can be produced by using a proprietary melting technique. The short wavelength cut on of this family of UV-transmitting glasses is similar to that of vitreous silica. In the present investigation the effect of broadband UV-radiation has been studied as a function of time and optical absorption primarily for the glass type UVFK-54. Further tests were performed using discrete line radiation of 248 nm from a pulsed excimer laser. The intensity of the darkening effect is correlated to the intensity and dose of radiation. In addition, recovery experiments using elevated temperatures and different times are discussed.

The solarization effects on the transmission of ten commonly utilized optical glasses and their counterparts are presented.

Short-Wave (SW)* ultraviolet transmitting filters that absorb visible light were obtained in 1985-86 from five manufacturers of filters and ultraviolet (UV) light assemblies. Two blind solarization tests were conducted in which 30 samples were evaluated to determine the effect of UV radiation on the filters over time. The radiation source consisted of two G30T8 germicidal lamps. The transmission of each filter was measured by a Perkin-Elmer Lambda 9 spectrophotometer at 253.7nm. The transmission of each filter sample was also periodically measured from 200nm to 800nm during the first test. The results of the solarization tests were then plotted as percent transmission at 253.7nm vs. hours of exposure to SW UV. The results demonstrate significant differences in solarization rate between SW filters.