Types Of Vitreous Silica Research Articles

Laser-induced bulk damage in various types of vitreous silica at 1064, 532, 355, and 266 nm: evidence of different damage mechanisms between 266-nm and longer wavelengths

Laser-induced-damage thresholds (LIDT's) with various types of vitreous silica at 1064, 532, 355, and 266 nm are investigated. At 1064 nm no difference in the LIDT was observed in any sample. At 1064-355 nm the wavelength dependence of the LIDT of synthetic fused silica (SFS) can be described well by the relation I(th) = 1.45lambda(0.43), where I(th) is the LIDT in J/cm2 and lambda is the wavelength in nanometers. At 266 nm, however, LIDT's were smaller than half of the calculated value from the relation above. This difference can be explained by the damage mechanism; at 266 nm two-photon absorption-induced defects lower the LIDT as in the case of KrF-excimer-laser-induced defects, whereas at longer wavelengths the two-photon process does not occur. LIDT's of fused quartz (FQ) at 532 and 355 nm and that of SFS containing approximately 1000 ppm of Cl and no OH at 355 nm were a little lower than those of the other SFS's. This lower LIDT may be related to the absorption of metallic impurities in FQ and dissolved Cl2 molecules in SFS. At 266 nm, on the other hand, LIDT's of FQ's were higher than those of most SFS's.

Local dynamic properties of vitreous silica probed by photoluminescence spectroscopy in the temperature range 300–4.5 K

We report experimental data on the thermal dependence, from room temperature to 4.5 K, of the photoluminescence activity in the spectral region between 4.0 and 4.5 eV, for different types of vitreous silica. The three photoluminescence bands previously detected in this energy range, α E, α I and α R, are investigated by analyzing the temperature dependence of their spectral moments. This method enables us to obtain information on both the electronic properties of the chromophores responsible for the observed emissions and on the structural and dynamic properties of their environment. Our results show that different point defects present different coupling constants with their surroundings and that the pristine properties of the silica samples is relevant in determining the structural heterogeneity and the mean frequencies of the vibrational modes that couple with the electronic transition.

Vacuum ultraviolet-induced strain in vitreous silica used for xenon lamp bulbs

Strain was generated by vacuum ultraviolet radiation in specimens of two types of vitreous silica (GE214 and Suprasil P20) in a xenon lamp. Strain energy calculated from the stress was linearly proportional to the energy fluence of the incident light. The density of the illuminated surface increased by about 1% over the density prior to illumination to a depth of ≤ 200 μm. This densification introduced a stress in the specimens. Point defects such as SiSi homo bond, E′ center, non-bridging oxygen hole center, SiOH and SiH were observed. Most of these microscopic structure changes occurred in the densified portion of the specimen in which the vacuum ultraviolet light, in the wavelength range 160–165 nm, was absorbed. The number of SiSi homo bonds in this layer was larger than the number of other defects generated. A linear relationship between the stress increase and the amount of SiSi homo bonds generated during illumination was observed. We assume that one of the origins of stress generation is the generation of SiSi homo bond. On the other hand, SiOH and SiH in the specimens decreased the magnitude of the stress. The occurrence of stress due to the SiSi homo bond generation and the stress depression by SiOH and SiH were identical within errors of measurement, in the two vitreous silicas.

Low-Temperature Thermal Expansion of Amorphous Solids

For most amorphous materials at temperatures below approx. = 1 K, the magnitudes and temperature dependences of specific heat, thermal conductivity and ultrasonic dispersion are qualitatively similar, independent of chemical composition. It has been suggested that thermal expansion also exhibits this universal behavior. The development of a dilatometer capable of resolving sample strains as small as 10/sup -12/ has permitted measurement of the linear thermal expansion of various glasses below 1 K. These investigations have demonstrated, however, that the low-temperature thermal expansion coefficient of glasses can be positive, negative, large or small. Analysis of measurements performed on two types of vitreous silica, two amorphous polymers, As/sub 2/S/sub 3/ and ZrO/sub 2/:Y/sub 2/O/sub 3/ is presented in the context of the phenomenological tunneling-states model. Consistency in explanation of thermal expansion and ultrasonic behavior is maintained by assuming a broad, weakly energy-dependent distribution of coupling strengths between phonons and the localized excitations thought to be characteristic of the glassy state.

Molecular diffusion and solubility of hydrogen isotopes in vitreous silica

Deuterium permeation, diffusion, and solubility measurements have been made for several types of vitreous silica at temperatures ranging from 0 to 800 °C. The activation energies for permeation and diffusion were found to be somewhat temperature dependent. Isotope exchange between structural hydroxyl and the diffusing deuterium was found to occur at temperatures ?300 °C. Certain types of vitreous silica also react with the diffusing gas to form metastable deuteroxyl at ?600 °C. Isothermal hydrogen-isotope solubility was shown to be described by the Langmuir adsorption isotherm at pressures up to 1400 atm, whereas the temperature dependence of hydrogen-isotope solubility was adequately described by a statistical-mechanics model. Combination of these two models leads to a universal expression for hydrogen solubility from 0 to 800 °C and from 0 to 1400 atm.

Helium Migration in Natural and Synthetic Vitreous Silica

Permeation, diffusion, and solubility of helium in several types of vitreous silica were measured. The activation energy for diffusion increases slightly with increasing hydroxyl concentration; no other significant trends were noted. These results are interpreted in terms of a random‐network structural model.