Borosilicate, potassium and sodium silicate and potassium borate glasses containing small quantities of AsO3 and 5½03 darken from the surface when exposed to H2 in the glass transformation range. The depth of surface darkening is a function of time, temperature, and H2 pressure. Change in absorbance at constant wavelength increases with time but shows neither linear nor square root dependence on time. In addition, the absorbance change (X constant) does not show Arrhenius behavior as a function of treatment temperature, but instead appears to approach saturation. The same phenomena are observed for D2 treatments. Absorbance change at 300 nm from the H2 treated sample under identical temperature and pressure conditions differs by a factor of the square root of 2. Relative permeability of H2 and D2 is given by the square root of their mass ratio, i.e. 12. This finding suggests a direct proportionality between the inducedabsorption and the permeability of the diffusing species. The coloration is attributed to the reduction of the fining agent (As/Sb) and is accompanied by an increase in the hydroxyl concentration in the glass. The effect of base glass permeability, fining agent identity and fming agent concentration on the optical absorption will be discussed. Metallic colloidal scattering is proposed as the mechanism for the coloration. Evidence to support the mechanism is presented and discussed.

GeS2 is known to be a good chalcogenide glass former with a transmission cut off at 1 1 . tm and has been studied for its application in the mid infrared region. The rare earth sulfides (La-Er) form reasonably good and stable glasses when mixed with other chalcogenides such as Ga2S3. In this work glass formation was studied in the GeS2- La2S3 system. Two compositions containing 60 mol and 92. 5 mol GeS2 respectively were studied and the effect of composition on the microstructure and thermal stability of these glasses were investigated. Microstructural analyses were performed on the as prepared and heat treated glasses using TEM and SEM/EDXA. Glasses rich in GeS2 exhibited primary (6-80 nm) and secondary (3-13 nm) phase seperation at the molecular level. Differential thermal analysis performed on these glasses indicated glass transition temperatures (Tg) of 590C and 420C for the two compositions studied. The glasses were stable and the (Tg) was observed to decrease with increasing contents of GeS2 in these glasses. 1.

Theoretically light transmission losses as low as lO3dB/Km are possible in optical fibers made from heavy metal fluoride glasses. One reason for this has not yet been achieved is scattering due to defects in the glass. A study of defects in ZrF4BaF2LaF3A1F3NaF (ZBLAN) glass has been carried out by laser light scattering tomography Leitz optical microscopy scanning electron microscopy energy dispersive spectroscopy and wavelength dispersive spectroscopy. Defects as light scattering centers were exhibited and their appearance dimensions and distribution were observed throughout the samples. The commonly found crystallites in this glass were identified to be LaF3 in different shapes and sizes. The formation mechanism and contribution of the defects to extrinsic scattering loss are discussed. 1 .

The refractive index of optical glass is typically measured using techniques based on the change of the direction light experiences after traveling through the sample; that is, using deflectoruetric methods such as: minimum deviation goniometry, critical angle procedures, moire deflectometry, etc. , (Ref.l) . On the other hand, interferometry has been used to evaluate the optical homogeneity of optical glass, as well as to determine the refractive index variation with temperature. In this work it is presented a method to measure the refractive index of optical glass samples using a holographic interferometer. This is an indirect technique in which the refractive index of the glass samples is measured by comparison with the refractive index of a reference liquid in which the sample is immersed. The presence of the reference fluid is used as well, to get higher values for the flatness tolerance on the working faces of the sample, and less precision in the measurement of the wedge angle. The values of the useful wedge angles depend on the fringe spacing value and the ruatching between the refractive index of the immersion fluid and the refractive index of the glass sample. The necessity of iaeasuring along a raininuirn distance given by the detector spacing and the accuracy needed for the measurement of fringe spacing, is discussed.

The degree of spatial variations of refractive index within a melt or blank is evaluated considering two paranieters: optical homogeneity and striae. The variations called striae correspond to strong inhoinogeneities of a very local nature. They produce a change on the propagation direction of light that is detected using schlieren techniques. Optical homogeneity corresponds to smooth spatial variations of the refractive index that produce negligible variations on the direction of propagation of light through the glass sample. Optical homogeneity is tested by transmission using classical interferomnetry (Ref . 1 , 2 , 3) . The wavefront transmitted through the sample is compared interferometrically with a reference wavefront. Hence conditions imposed on the quality of the optics used in these instruments are strong. The sample itself must be well polished or convenientely tested to separate its surface deformations from the contribution due to optical homogeneity. In this work it is presented the analysis of an holographic technique applied to the assessment of the honogeneity of optical glass plates. It is used an inunersion device to avoid the need for separating surface contributions. Optical homogeneity can be determined from a single interferogran, against the two (Ref . 3) , or four (Ref . 1 , 2) needed when using classical interferometry. It is shown here that this holographic interferornetry method has a higher accuracy.

We report the interaction of sub-band gap 5. 0 eV (KrF) laser irradiation with intrinsic defects in Type III and IV silica. The silicas were divided into two groups for laser interaction studies. One group was first irradiated with 137Cs to a dose of 6. 6 x iO?'' rads. The second group was irradiated with laser light in the as-received state. Optical absorptions of the samples from 3 to 6 eV were measured before and after 200 300 700 and 1500 pulses (l90mJ/pulse-cm2) of KrF laser light. Neither optical bands nor EPR spectra were observed in the as-received silicas. The spectra of samples pre-irradiated with 137Cs contained components due to peroxy radicals non-bridging oxygen hole centers E''centers and E" centers. The concentrations of these defects were dependent upon silica type. Subsequent laser irradiation of the gamma-ray irradiated samples bleached bands at 5. 4 and 4. 8 eV in type III and type IV silica respectively. The EPR spectra showed that laser irradiation bleached the peroxy radical and produced a new oxygen related center (ORC) in type IV silica. No detectable change in the non-bridging oxygen hole center concentration in the type III silica samples were observed. E'' center concentration increased. For the same laser irradiations the concentration of E'' centers produced in the as-received samples was a factor --''20 less than in the samples first irradiated with 137Cs. We suggest that

Transient and permanent UV absorption bands and fluorescence bands induced by 248 nm excimer laser radiation in fused silica are reported. It is shown that the permanent absorption measurements are not suitable to characterize the material with respect to transmission of high power laser pulses. In fused silica samples with high OH - content recovery of the 210 nm absorption band is observed after the end of irradiation. In samples with low OH - content no quick re covery is observed. 1 .

Highpurity silica glasses prepared by various manufacturing methods were investigated after irradiation with an ArF excimer laser. Defect species and concentrations were found to be dependent on oxygen stoichiometry and impurities: E'' centers are induced in oxygendeficient high-OH silica at concentrations of 1O''6/cm3 while at one or two orders of lower concentrations in other types of samples. Defect centers in yirradiated silicas studied for comparison show a similar dependency on oxygen stoichiometry and impurities. In addition O ions are observed in oxygensurplus samples after yirradiation which were creates presumably by the trapping of free electrons. Isochronal annealing experiments indicate that the annealing of E'' centers in ArFlaser irradiated samples are due to the diffusion of 02 and H20. 1 .

This report summarizes an investigation of new luminescent glasses for use as x-ray-tolight conversion imaging media for x-ray radiographic applications. Luminescent activators such as T b3+ Eu2+ and Ce3+ were investigated in high density 3 g/cm3) high z fluoroborate fluoride borate and silicate host glasses. Terbium activation in each of these materials has at least a factor of 2 higher luminescent response under x-rays than either of the other two activators. The selection of the host material has a large effect on the luminescence characteristics. Terbium activated silicate glasses have a luminescent response 3 times higher than any of the other terbium activated glass materials investigated. The addition of Gd3 to terbium activated silicate glass has been shown to improve the x-ray-to-light conversion efficiency by as much as a factor of 1. 2 for this glass material. This increase in efficiency most likely occurs because of a Gd3+ Tb3 energy transfer process. 1.

The behaviour of gammairradiated radiation shielding glasses has been investigated. With increasing density of the glasses the attenuation of the radiation and the energy deposition in the glasses increase. The lower the radiation energy the higher the energy deposition per unit volume of glass and therefore the stronger the observed discolouration. Comparable discolouration appears in glasses of density 4 g/cm3 if the irradiation dose of a Co-60 source (1 MeV) is a factor 6 higher than an Ir-192 gamma source (0 MeV) 1.

Photonucleation has been studied previously in glasses in the lithium silicate system. In this work it was intended to extend this phenomenon to the lithium aluminosilicate system in order to crystallize /3-spodumene only. Various glass compositions with alumina content varying from 10 to 25 wt. were investigated. Glass batches were mixed with water to form a slurry completely dried and then melted. Glass was then exposed to UV radiation and subsequently heat treated. When prepared in this manner photonucleation was not obtained for these systems containing higher amounts of alumina. However when the slurry was allowed to form a wet but firm mixture and then melted the resulting glass exhibited the photonucleation effect. The results are explained in terms of the oxidative nature of water in silicate batches and melts. 1

Interest in nonlinear optics has been growing rapidly. Today many materials are known to possess nonlinear effects and the intense search for even more efficient and cost-effective materials is continuing. Various crystals are known for large nonlinear coefficients however their limitations in size and high cost make other solid state materials such as glass more attractive despite their relatively smaller non-linear coefficients. We review the research on glasses with high nonlinearity by classifying them into homogenous type and heterogeneous type. 1.

Quantum confinement effects of semiconductor microcrystallites (CuC1) embedded in a glassy (aluminoborosilicate) matrix are of current interest due to their exceptional nonlinear optical properties. The precipitation of microcrystals occurs upon heat-treatment of a glass in a supersaturated solution. The time and/or temperature of heat-treatment and the degree of supersaturation of the solution determines the size of the microcrystals. This paper characterizes the microcrystals using TEM when the heat-treatment conditions are varied. Room temperature ESR measurements were performed in order to determine the ratio of Cu2 to Cu'' in the glass at various compositions before heat-treatment. Low temperature optical absorption data were jobtained to study the quantum confinement and the effect of varying the microcrystal size. I.

We used picosecond degenerate four-wave mixing technique to study acoustic properties of the laser induced ultrasonic sound wave in optical filter glasses. Ultrasonic velocity and absorption were measured over the frequency range of (100 MHz -20 GHz) we found the frequency dependence of the acoustic absorption in these filter glass are in quantitative disagreement with the prediction of the two-level system relaxation model. In additional to sound velocity and absorption coefficients various of photoelastic and thermal optical constants of the optical glass materials can be determined accurately by this method.

Our laboratory recently has announced the formation of glasses based on the oxides of lead bismuth and gallium. These glasses are unusual in that they contain none of the traditional glass-forming caflons (eg. silicon boron germanium or phosphorous) yet exhibit a remarkable stability. In addition to this stability these compositions exhibit some rather unique properties such as the ability to transmit well into the infrared region (to about 8 microns) and a high nonresonant optical nonlinearity 3 (of 42 xlO 14 esu). To take advantage of this latter property for optical switching applications it is desirable to prepare the glass as an optical waveguide. Silica additions were made to a heavy metal oxide base glass in an effort to derive compositions suitable for core and cladding. The present paper describes the effects of these additions. 1.

The glass forming regions of the Bi015-CuO-Ca05Sr05O superconducting system have been explored by the addition of PbO. The glass froming regions expand with PbO addition and shrink with the substitution of copper oxide by zinc oxide. The glass transition temperature of these glasses ranges from 300C to 420C. These glasses have high refractive index of about 2. 8 and density from 6 to 9 g/cm3 they are infrared transmitting with cutoff wavelength farther than 7 tm. The high polarizability of Bi3 ions gives these glasses high non-linear optical coefficient of 4 * lO13. 1.

18642 With the development of new bright narrow line sources in the form of lasers (see Table I) and better detectors the classical concept of optical glass has been expanded to include new glasses for applications in the ultraviolet and the infrared spectral regions. I would like to review briefly some recent developments in the spectral range from far UV to the end of the atmospheric window at 12 2 .

Heavy metal fluoride glasses are of particular interest for laser window applications because they have negative thermo-optic coefficients dn/dT. A negative value of dn/dT leads to very low to near zero optical path distortion (OPD). Because heavy metal fluoride glasses are multi-component glass forming systems they offer a means to tailor properties through compositional variations in such a way that OPD can be controlled and minimized. This paper examines the effect of compositional changes of ZrF4 -based glasses on properties critical in determining OPD i. e. thermal expansion refractive index and dn/dT. In addition this paper describes a new interferometric technique used to measure CTE and dn/dT concurrently. The role various components play in determining the critical properties and the theoretical OPD is discussed. Finally the viability of using these compositional changes for the preparation of bulk glasses will be evaluated in terms of glass stability. 1.

Calcium aluminate glasses are transparent to a longer wavelength than silicate gI asses. However it is well known that they are difficult to form into conventional optics due to their high tendency to crystallize. To increase the understanding of aluminate glasses a study of the effect of small silica additions on such properties as viscosity and crystallization tendency has been combined with a study of such optical properties as infrared cut-off and UVVis-NIR spectroscopy. 1.

Raman and x-ray photoelectron spectroscopy are used to characterize the effects of fluorine incorporation on the short range structures of several simple phosphate glasses. Fluorine depolymerizes the chain structure of NaPO3 by replacing bridging POP bonds with terminal PF species. In aluminophosphate glasses with small fluorine contents fluorine is primarily associated with aluminum. When the fluorine to aluminum ratio exceeds three the number of Al-F bonds are maximized and significant numbers of P-F bonds form. 2.

Neodymium doped vitreous silica was prepared by the sol-gel method. We report optical properties fluorescence lifetimes and microstructure of glasses containing as much as 5. 0 wt neodymia. Some of the spectral features are discussed and compared with those of glasses containing neodymia which are known to show laser action. 1.

The Ml I erWede Goni ometer-Spectrometer Model 2 is a medi urn-high accuracy instrument for the determination of prism angles and index of refraction in the visible wavelength range (400-700nrn) With its automatic Heidenhain rotary encoder the instrument is capab''e of absolute accuracy to I O arcsec for prism angle measurements and i x I 05 for index of refraction measurements. Recently we have developed a modified version of this instrument to provide absolute index of refraction measurements in the wavelength range from the UV through the near IR (254nm-2325 nm). The absolute accuracy for index of refraction measurements in the range is j INIRQDILTIQt4 The classical methods of Rudberg and Franhoer are still the most accurate means of determining the absolute index oT refraction or bulk optical materials. Both methods utilize a collimator and telescope pair which are both focused at inflnity. The former is normally flxed and the latter is mounted on a goniometer arm equipped with a precision graduated circle to provide absolute angular position of the telescope. The collimator is used to project the slit image o various spectral lines through a prism made from the material to be tested Usually spectral lamps are used for the light sources but lasers have also been used. The telescope and the sample prism are each rotated about the vertical axis of the goniometer so that each is set at proper angle to produce a minimum angle of deflection of the projected slit image with the desired wavelength. The goniometer arm and telescope are then fine-adjusted so that the slit image 32 / SPIE Vol. 1327 Properties and Characteristics of Optical Glass II (1990)

Fluorozirconate glass compositions were irradiated with 1 . 1 73 and 1. 333 MeV gamma-rays from a cobalt-60 source to study the influence which fluorine network concentrations sodium doping indium doping cobalt doping cerium doping have on radiation damage. Lower concentrations of nonbridging fluorine ions were found to reduce color-center absorption and indium doping was found to eliminate visible and infrared radiation-induced colorization. 1.

The refractive index n is known to vary with the temperature. Thus the optical path length and the focusing properties of transmissive optical elements may change with the ambient temperature T. Since there was no reliable dispersion formula of the temperature coefficient dn/dT the manufacturers of optical glasses published data on dn/dT averaged over certain intervals ( +i). These data are available for a small number of discrete wavelengths )k only. To calculate numerically n as a function of T for wavelengths other than ZAk one has to inter polate and to integrate over different intervals of T with the respective average data of dn/dT. In order to avoid this awkward procedure and to reduce the necessary data used for numerical calculations a dispersion formula for dn/dT is developed on the basis of a simple model. This formula has been tested and applied successfully to experimental data of dn/dT both as a function of wavelength ) and of temperature T for more than 140 different opti cal glasses in the visible spectral region and in the range of 400C T 800C. For 22 glasses data are available also for an extended range of temperature _1000C T 1400C. Even in this case the dispersion formula can be applied successfully. Moreover this formula can be integrated easily as a function of T to give immediately the increment of the refrac

A series of glasses with low thermal expansion has been studied for the purpose of developing a mirror substrate. One particular composition has been found to have desirable optical fabrication characteristics of ease of grinding and polishing. The approach in tailoring the thermal expansion with the chemical composition is explained. 1.

The use of fluorophosphate glasses for transmission in the mid IR and as optical fibers have been attempted for the first time. These materials are easy to prepare and are of relatively low cost. They can be attractively compared to either chalcogenide or heavy metal fluoride glasses for midIR transmission. Preparation techniques mechanical and optical properties are reported. 1 .