Eastman Kodak Company included twelve substrate and coating samples on the LDEF structure. There were three fused silica and three ultra low expansion (ULETM) uncoated glass samples, two ULETM samples with a high reflectance silver coating, two fused silica samples with an antireflectance coating, and two fused silica samples with a solar rejection coating. A set of duplicate control samples was also manufactured and stored in a controlled environment for comparison purposes. Kodak's samples were included as a subset of the Georgia Institute of Technology tray, which was located on row 5-E, tray SOO50-2. This placed the samples on the trailing edge of the structure, which protected them from the effects of atomic oxygen bombardment. An evaluation of the flight samples for effects from the 5 year mission showed that a contaminant was deposited on the samples, a micrometeroid impact occurred on one of the samples, and the radiation darkening which was expected for the glass did not occur. The results are listed below in more detail.
With the increasing complexity and precision of space-based optical systems and their longer intended lives, the effects of the space environment upon optical system reliability are becoming more important. Previously neglected phenomena pose potential threats to the success of current and future missions involving optical instruments. This paper presents a review of issues related to the reliability and quality assurance of space optics systems. Descriptions of hostile environments and mechanisms of damage are presented. Methods used to harden past and present optical systems against environmental effects are surveyed and their relative efficacies are discussed. Suggestions for actions by reliability and quality assurance personnel to mitigate the risk to future missions are outlined.
Effects of 1 MeV electron and 5 MeV proton radiation on the optical transmittance of glass materials have been examined. Room temperature annealing of the radiation-induced transmission loss have been monitored. Results indicate that glass materials have different recovery rates.
The ability of optical seeker/sensor systems to acquire, discriminate, and lock on to their targets is essential to the success of all interceptor systems. A telescope primary mirror is highly vulnerable to x-ray exposure, which may result in increased scatter as well as permanent and/or transient distortion. Interceptor target discrimination and tracking is thus compromised. We have fielded several experiments to examine the effects of nuclear radiation on a variety of mirror samples representing those technologies which might be applicable for an optical sensor/seeker system. Mirror deformation and scatter measurements were performed in real-time, providing dynamic response and recovery data. Post-test measurements included scatter, reflectance, and permanent distortion as well as microscopic examination of the mirror surfaces. Results from these experiments are presented along with comparisons to analytical models.
Proton induced absorption over the 350 nm to 2500 nm spectral region and the growth of that absorption with increasing dosage was determined for four glasses (Schott glasses FK3, SF57, IRG7, and Corning Glass Works fused silica 7940). For FK3 and SF57 we can compare the proton induced absorption with x- ray induced absorption. We found protons induced less absorption than x rays for comparable doses by a factor that depended on the glass. Annealing effects with time were also observed. The results indicate that reliance on x ray or electron dosage data overestimates the amount of induced absorption that will occur under realistic orbital conditions where protons dominate the dose. We also searched for proton dose induced index of refraction changes in the glasses, and were able to place an upper limit on the change in n of 10-4. This shows that a prism spectrometer is a feasible candidate for spaceborne observations. The absorption in a holmium oxide filter glass and an optical cement also was characterized.
A test apparatus to perform in-situ, real-time radiation effects testing of infrared bandpass filters has been designed, fabricated, and fielded. The apparatus measures transmission and waveband shifts of IR filters at cryogenic temperatures. We have performed prompt gamma radiation testing and have analyzed the data and developed models explaining the response.
Much recent data from the Long Duration Exposure Facility (LDEF) have confirmed that for multiyear periods in low earth orbit (LEO) many satellite surfaces (especially the leading edge, or RAM) are subjected to significant bombardment by small particles in the 1 to 100 micron size domain. These particles are both micrometeoroids and man-made debris. Of interest is the consequential effects on precision surfaces such as high-resolution optics. The damage produced does not necessarily seriously downgrade the reflectivity (for mirrors) or transmissivity (for lenses), but can significantly worsen optical scatter. Since many optics are not simple metal mirrors, for which the major response is near-hemispherical cratering, but are frequently comprised of brittle dielectrics (including multilayer coatings) which suffer conchoidal cratering, star cracking, and interlayer differential delamination, the correlation between the induced mechanical damage and the resulting optical scatter is complex. An approach is given which attempts to analytically predict the material damage modes for various impact conditions, and also correlate this damage with optical scatter.
This paper describes radiation and drop testing performed in support of the U.S. Army Strategic Defense Command's program to develop more robust baffle materials. It gives the shock and vibration environments and describes the techniques used to capture and count the particles generated. Also, observations are made on the effect of shock and radiation on the optical performance of the baffle materials.
The incidence of energetic photons, electrons, and heavy particles on surfaces of optical components leads to the generation of surprisingly intense radioluminescence which may interfere with sensor performance. This research focuses on the ways in which energy is deposited by incident electrons leading to fluorescence, bond-making and bond-breaking processes on surfaces and in the near-surface bulk. Knowledge of these microscopic mechanisms provides detailed clues which lead to an understanding of macroscopic processes, such as surface glow, materials modification and darkening. We describe progress in ongoing studies to determine the influence of substrate material, temperature, and cryolayer species on the intensity and the decay time of electron-induced glow, and the related phenomena leading to darkening, of optical components. Emphasis is on the identification of mechanisms responsible for both glow and darkening.
A model of the midcourse space experiment (MSX) spacecraft and its electromagnetic environment has been developed using the potential of large spacecraft in the Auroral region (POLAR) code. The geometric model has a resolution of 0.341 meters and uses six materials to simulate the electrical surface properties of MSX. The vehicle model includes features such as the major instruments, electronic boxes, radiators, a dewar and open bay, a booster attachment ring, and three different orientations of the solar panels. The electron and ion composition and temperature environment are modeled as a function of the solar activity. Additional parameters include the ram-wake orientation, the hot electron spectrum, day-night-twilight variations, latitudinal variations, and solar panel voltage biasing. Nominal low spacecraft charging cases are described. Calculation with a high peak energetic electron flux produces a ground potential of -180 volts and differential charging as high as 66 volts.
Formulas exist for prediction of diffusion limited outgassing rates under isothermal conditions. An algorithm has now been developed that predicts outgassing rates for material species that outgas via diffusion mechanisms for non-isothermal conditions. The algorithm uses initial species mass, diffusion coefficient, activation energy and a temperature history to determine outgassing rates at prescribed times. The algorithm accounts for bulk material temperature variations through time but does not account for thermal gradients through the material thickness. The non-isothermal mass loss equation is derived from a basic isothermal mass loss equation with the term that indicates species molecular propagation for the non-isothermal conditions. For isothermal conditions, the product of D(T) (where temperature T, is constant) and time is a measure of the species molecular propagation. This term in the isothermal mass loss equation is replaced with the term for non-isothermal molecular propagation, which is the integral over time of D(T) (where temperature, T, is time dependent). Temperature dependent outgassing rates are calculated by numerically differentiating the time and temperature dependent mass loss predictions. Mass loss rates for the non-isothermal conditions are compared to isothermal mass loss rates.
Partial pressure or residual gas analyzers are often invaluable for materials and contamination studies. However, some instrument design features and combination of operating parameters can cause performance features quite different from what many users expect. These unexpected performance characteristics can include pressure-dependent sensitivities, the sensitivity for one gas depending on the pressures of other gases, and time-dependent sensitivities after operation with gases such as oxygen or water. These characteristics can greatly complicate instrument calibration and can cause errors as large as two orders of magnitude. This paper discusses measured performance characteristics for different partial pressure analyzers that illustrate a wide range of performances from the different instruments, as well as several features that seem to be common to most instruments.
Sputtering yield measurements, which help to quantify the rate at which erosion occurs, were made for low-energy beams (50 - 200 eV) of O+, O2+, N+, and N2+ incident on Al, and Al2O3 surfaces. These materials are likely candidates for exterior portions of Space Station Freedom's power generation system. Potential differences produced by the power generation system (possibly as high as 300 volts) would accelerate the ions in the surrounding plasma to energies well above the sputtering threshold. Atomic oxygen and molecular nitrogen interactions with surfaces play a critical role in surface erosion and space glow that occur for exposed materials in a low-earth orbit. As much as 90% of the atmosphere at these altitudes is comprised of atomic oxygen which is more abundant than the molecular form since the molecular form is quickly dissociated by UV radiation. Mass-loss measurements were conducted using samples that were vacuum deposited on the surface of a quartz crystal and a novel technique was utilized to increase the sensitivity of the quartz crystal microbalance which was used to measure the mass loss.
The surface finishing of x-ray grazing incidence optics is the most demanding area of optical processing, both in terms of metrology and application of optical finishing techniques. This paper discusses the application of specialized metrology and finishing techniques in producing a low x-ray scatter grazing incidence telescope.
The range of optical and thermal properties offered by Nd-doped phosphate glasses allows these materials to service a variety of laser applications. For example, the high extraction efficiency, low non-linear index and superb optical quality render Nd:phosphate glasses suitable for large-scale fusion laser technology. In this case laser efficiency as well as cost and glass yield issues are critical. As a consequence of the very low repetition rate (< 1/hour), however, issues surrounding thermal fracture during laser operation are not important. On the other hand, high and moderate-average power laser systems require that the active element performs well under substantial heat loading. Here, the most important issues involve the thermal properties of the medium, and design considerations suggest that it is worthwhile to have somewhat lower extraction efficiency if the material can be engineered to endure significantly more heat loading without thermal fracture. It has been observed that the Nd:phosphate composition space spans thermal figure-of-merit and emission cross section values exceeding a factor of two. It turns out, unfortunately, that improved thermal properties tend to be roughly correlated with inferior laser attributes. In addition to the laser and thermal properties many other property issues need to be addressed including devitrification, durability, and platinum solubility. The manner in which the glass constituents affect glass properties and the nature of the trade-offs that are encountered in engineering practical media are discussed.
The polarity of the silica cage has been investigated by entrapping organic dyes in a silica gel. pH dyes of bromocresol purple and bromocresol green were selected for this study. The influence of pH on the polarity of the silica cage was determined by measuring the spectral shift of the dye. The pH dye- impregnated silica films show a red-shift in an acidic environment and a blue shift in basic environment, compared to those dissolved in water. This implies that the polarity of a silica cage varies after being treated by different pH solutions. The cage shows higher polarity in a basic solution than in an acidic solution.
Ion implantation of Cu in high purity silica has been used to produce nanometer size metallic copper clusters. The size and size distribution of these colloids have been characterized by quantitative images analysis emphasizing transmission electron microscopy. Electron diffraction patterns indicate they are crystalline FCC copper embedded in the amorphous silica host. The ion implantation dose and substrate temperatures alter the size distribution of the colloidal copper. The optical transmission of implanted silica containing varying sizes and size distributions of Cu clusters has been determined and is related to the size distribution.
Infrared reflectance between 4000 and 100 cm-1 and optical spectra between 1.8 and 6.2 eV of high purity silica implanted with nominal doses of 1, 3, and 6 X 1016 Pb ions/cm2 were recorded before and after annealing at 400, 600, and 800 degree(s) C for 1 hour. Curve resolution analysis of the Si-O stretching region resulted in six peaks which were characterized by their lineshape parameters. The oscillator strength of the ion induced defect peak at 1035 cm-1 was found to depend on ion dose. The defect band at 1035 cm-1 decreased to an intensity comparable to that of the unimplanted glass after thermal annealing for 1 hour at 800 degree(s) C. Far infrared spectra indicated the formation of lead silicate particles after annealing.
The physical elongation of a phase-separated glass by the application of a pulling stress to the glass above its softening temperature leads to a material with a number of interesting optical properties. This study is concerned with silver halide as the separated phase in an alkali-alumino- borosilicate glass. The initially spherically shaped halide particle is elongated into an elliptical shape by the action of the stretching process. As a consequence, the composite body acquires optical anisotropy exhibited as birefringence and dichroism. Experimental results show how the magnitude of the optical anisotropy can be related to shape anisotropy of the particles and, in turn, to the pulling stress. These results are discussed in terms of a simple polarizability model which adequately explains the results.
The structural model of fluoride phosphate glasses can be described as Al(F,O)6-octahedral chains bonding by mono- and diphosphate groups and cations. Proofs are given of Raman and NMR spectroscopy. These glasses posses special optical properties making them attractive candidates for application in high performance optics. UV transmittance, solarization, and luminescence properties were investigated. Glasses melted under reducing conditions show high UV transmittance, only small solarization effects after irradiation at 248 nm, but high effects at 193 nm. Glasses doped with 75 ppm Ce yield higher solarization effects than glasses without cerium ions. After irradiation the Ce3+ luminescence has nearly vanished.
This study obtain many excellent properties of glass with high refractive index(ndl. 7779,flF— n0=O. 01552)on the basis of VD==50. 1 ,acid resistance class lb and moist resistance class A as a result of designing new formulation and applying new technical and controlling structure and overcoming crystallization and updating rare earth optical glasses available. The group structural model of RmOn RE203-Al203-Si02-B203 multicomponent system is put forward first time as Fig. 1. The model is proved by X-ray diffracion,DTA,Crystallization activation energy,IR spectrum,Raman spectrum,XPS spectrum ,NMR,EXAFS etc. A series of structural data is obtained.
Only a limited number of optical glasses are commercially available that can be used in high-fluence laser applications between 0.35 and 1.05 micrometers . These include, primarily, certain phosphate glasses and fused silica. Phosphate glasses can now be made free of Pt-inclusions; the technology leading to this improvement is briefly discussed. In addition, inclusion-free fused silica can be made by a high temperature, chemical-vapor-deposition (CVD) process. Measured damage thresholds over a range of wavelengths and pulse lengths are reported for these materials. In addition, the use of doped layers of plasma CVD fused silica as a means of making high-damage-threshold rugate filters is presented. The impact of a high nonlinear refractive index (n2) on the spatial profile of the laser beam is discussed. Dramatic improvements in laser performance are possible if an inclusion-free, low-n2 glass (such as fluorophosphate) could be made. Multiphoton absorption and solarization of fused silica at 351 nm are also reviewed; fused silica continues to be the preferred material for high fluence applications at this wavelength.
Some special minor, but also main, glass components are photochemically sensitive substances. After being exposed to DUV-radiation glasses can show solarization, fluorescence, and defect absorption phenomena. A new alumina boron crown glass family based on oxidic components has good potentials for all applications of UV optical systems and also photochemical technology processes. In this brief paper we discuss by means of a model glass systems special effects in ultrapure glasses melted under reducing conditions. Irradiated glasses showed a strong dependence of solarization on the specific glass composition. A KrF excimer laser of Jenoptik GmbH Jena was used as an excitation source. Doses of 25 - 80 J/cm2 were tested. Three characteristic defect absorption bands were observed in alumina boron crown glasses having iron impurities less than 5 ppm melted under reducing conditions. Excitation into the wavelength of maximum absorption causes characteristic fluorescence. Correlations to structural units with the help of RAMAN and NMR spectroscopy techniques are discussed.
Faraday rotator glasses with high Verdet constants are used for optical isolators and sensors. Based on the Tb2O3 -B2O3-Al2O3- SiO2 system and the effect of each component on glass formation, glass compositions were selected for development of new Faraday rotator glasses. Devitrification of Tb-glass was studied by microscopic morphology to establish the production process. Dispersion of Verdet constant and the influence of Tb3+ concentration on Verdet constant were investigated. Special technology was utilized for production of platinum-free glass. The quenching process is necessary to obtain crystal-free glass. Three kinds of Faraday rotator glass with higher Verdet constant than that of M16 have been developed. The higher Verdet constant glass is possible to obtain.
Ultraviolet laser radiation induces a myriad of effects in silica glasses and fibers. This study deals with the absorption and luminescence characteristics of silica manufactured by different methods, containing varying amounts of water -- broadly grouped into the ultra dry, moderately wet, and very wet types. The effect of 248 nm (KrF) excimer laser radiation on these characteristics is examined. The effects seen in the bulk form are contrasted with those seen in drawn fibers, in particular, with regards to the luminescence behavior.
A study of the effects of Co60 gamma radiation on the transmission and index of refraction of several optical glass types is presented. The glasses have indices (nd) in the range of 1.486 to 1.581. They are multicomponent glasses from different families. UV-transmitting glasses having lower impurity levels are compared to the standard optical glasses. Transmission spectra in the range of 190 - 820 nm were recorded after exposure to various doses of radiation up to 725 krad. In all samples, the UV transmission edge shifted towards longer wavelengths and the visible transmission decreased. Differences in transmission spectra were observed depending on the glass composition and impurity levels. Fading curves of some glasses irradiated with different doses of gamma radiation were studied at room temperature and after heat treatment of 400 degree(s) C or 500 degree(s) C. At room temperature a slight recovery with time was observed. One fluorophosphate glass type recovered nearly completely after heating for a few hours. The effects of impurities on recovery is discussed.
For some twenty plus years, infrared glasses have been one of the coming new materials. They have always had a lot of promise but, except for some military applications of bulk components, infrared glasses have not been commercialized. There is now a new wave of attempted commercialization with groups in France, and the USA building embryonic businesses in heavy metal fluoride fibers, and groups in Japan, USA, and Russia beginning to develop marketable chalcogenide fiber. Some work is also being done with modeled chalcogenide glass lenses. The major applications for the fiber are chemical sensing (spectroscopy), temperature sensing (pyrometry), and low-level laser power delivery. Telecommunications and long lengths of ultra-low loss fiber are not a significant factor in today's market, indeed the loss requirements for most applications are in the 100s of dB/km. Even at those levels, however, heroic efforts of raw material purification are often required to obtain the necessary properties. All infrared glasses have characteristics that make them more difficult to work with than conventional glasses. Against this is the advantage that these materials, to a greater or lesser extent, transmit in the infrared region of the spectrum and may be used to make fibers or optical components with characteristics that are otherwise not available.
Historically, optical glasses were developed to provide desired optical characteristics; specifically, refractive index and dispersion. The batch composition required to achieve the optical performance demanded by industry sometimes resulted in glasses with weak chemical resistance. Due to the many different chemical constituents found in optical glass, it is impossible to define a single test method which can suffice as a means of describing the chemical behavior of all glasses. Since even a slight attack of the surface layer can render the optical element totally useless, the processor must gather and evaluate all the information available concerning the chemical behavior of the glass in order to minimize the risk of disastrous surface changes during processing.
Modern optical design requires measurement of the refractive index of optical glass to the sixth or the seventh decimal place. Reflectometry represents an interesting option to go beyond the fifth decimal place, since from the literature we know that this technique can work to the fifth decimal place. In addition to that, this method does not use a large area of the sample, a condition that helps to increase the contribution of systematic errors. The techniques used to determine the refractive index of optical materials include transmission and reflection methods. The highest accuracy transmission techniques used in refractometry are: minimum deviation and critical angle goniometry, moire deflectometry, and interferometry. The main systematic errors that limit the measuring accuracy of each of these techniques are mentioned. The techniques used for the determination of the refractive index of optical materials from measurements of the ratio of the reflectance coefficients of its surface are widely used. Many of these methods rest on simplifications of Fresnel equations at specific angles of incidence. The geometries used include: normal incidence, 45 degree(s), Brewster angle, and other angular positions related with the specific sample to be evaluated. The analyses reported in the literature contain just the parameters present in the simplified formulas obtained for the Fresnel coefficients of each specific configuration. In this work a more complete analysis of these techniques is presented.
The formation ranges of glasses in Mn02—Li20—P305 system have been experimented. The glass structure, valence and coordination number of manganese have been investigated by X—ray photo— electrical spectroscopy(XPS) infrared spectroscopy(IR) Rarnan spectroscopy and visible spectro scopy. The results have shown that some Mn ions iiay be in four-fold coordination and enter the glass network. Valence and coordination number of manganese and colour have also been discussed. The mang anese(1I) is pale yellow and is six-fold octahadron coordination. The manganese(Ill) is purples bluish—pink or brown and is predominantly in six—fold coordination. However the Mn—O bonds be— come more covalent with increasing Mn02 or MrtO2—Li20 content in MnO2-P2O and Mn02-Li20—P205 system.
The dynamic fracture of pure aluminum targets with thickness in the range of 100 to approximately 800 micrometers has been investigated experimentally under shock loading induced by Nd:glass laser pulses of 4 ns FWHM. The experimental results indicate that the spallation of aluminum at ultra high strain rate up to 107s-1 is still a ductile fracture in the way of voids' nucleation, growth, and coalescence in interior of the material, but the damage behavior is somewhat different from that obtained by ordinary loading methods at lower strain rate. The function of spall thickness versus the target thickness is nearly linear under the conditions of this experiment.