Showing papers by "E. J. Friebele published in 1979"

Oxygen-associated trapped-hole centers in high-purity fused silicas

Abstract: Two distinct oxygen-associated trapped-hole centers (OHCs) are identified in samples of room-temperature γ-irradiated, high-purity fused silica. One, which we label the “wet” OHC, predominates in the high-OH-content (wet) silicas while the other, the “dry” OHC, is more prevalent in low-OH (dry) silicas. Excellent computer simulations of the low-temperature electron-spin-resonance spectra are obtained for both wet and dry silicas using only the relative abundance of the “wet” and “dry” OHCs as an adjustable parameter. Analysis of the 17 O-hyperfine structure which occrs in samples of wet silica enriched in 17 O provides direct confirmation that the “wet” OHC is a hole trapped in a single nonbonding 2p-orbital of an oxygen (presumed nonbridging). Correlation of optical absorption and electron spin resonance via isochronal pulse anneals indicates that the “dry” OHC has an optical transition ay 7.6 eV. In addition, it is reported that the “dry” OHC can be induced in the dry silicas by the fiber drawing process. From the present results, an O 2 − molecular ion model appears most attractive for the “dry” OHC.

Fundamental Defect Centers in Glass: The Peroxy Radical in Irradiated, High-Purity, Fused Silica

Abstract: A new fundamental radiation-induced defect in high-purity synthetic silica has been identified by electron-spin-resonance studies of $^{17}\mathrm{O}$-enriched Si${\mathrm{O}}_{2}$ as a peroxy radical ${\mathrm{O}}_{2}^{\ensuremath{-}}$ bonded to one Si in the glass matrix. The precursors of these defects are envisioned to be \ensuremath{\equiv} Si-O-O-Si \ensuremath{\equiv} structures, some of which preexist in the silica, are formed in greater numbers during neutron bombardment, and which may release an electron either during irradiation or subsequent annealing.

Ferromagnetic resonance of spherical particles of α‐iron precipitated in fused silica

Abstract: Ferromagnetic resonance (FMR) spectra were obtained at 9 and 35 GHz for particles of metallic iron precipitated in fused silica containing 1–120 ppm Fe. Accurate g values and anisotropy constants K1, K2 and K3 were extracted by computer simulation of the powder pattern line shapes, assuming negligible shape anisotropy. One sample, melted under a He‐H2O atmosphere, exhibited anisotropy constants identical with published values for pure α–iron and a g value of 2.081±0.002. Samples strongly reduced in H2 displayed smaller values of K1, consistent with expectation for alloying of the Fe with up to 20% Si. These K1 values were shown to be statistically distributed and linearly correlated with the g values in the range 5?at.%Si?20. All samples displayed increases ∼ 5–10% in apparent K1 value with increasing frequency, either as‐delivered or after aging. It is hypothesized that the latter effects are due to the formation of a magnetic iron oxide layer at the metal‐glass interface.

The effects of impurities upon photoluminescence and optically induced paramagnetic states in chalcogenide glasses

Abstract: Photoluminescence (PL) and optically induced electron spin resonance (ESR) have been studied in As2Se3 glasses doped with Cu, Tl, I, Ag, In, and K and in B-doped As2S3 glass. In all cases there is no significant change in PL efficiency or intensity of induced ESR until dopant concentrations exceed ∼1 at.%. These results are in marked contrast the strong dependence of transient hole transport upon dopant concentration in the same glasses. These parallel but contrasting observations are discussed in terms of the predicted effects of dopants on defects in chalcogenide glasses postulated by Mott on the basis of the charged defect model of Mott, Davis and Street (MDS). PL and ESR studies of the AsSe glass system have revealed that oxygen contamination can severely quench PL efficiency and ESR intensity for As concentrations

Radiation Response of Large Core Polymer Clad Silica Optical Fibers

Abstract: The radiation-induced optical losses in a selected group of large diameter polymer-clad silica (PCS) optical fibers has been measured in both steady state and pulsed radiation environments. Fibers typically were fabricated from radiation resistant synthetic silicas and silicone polymer materials. Measurements were made in situ at room temperature for operational wavelengths of 0.82?m and 0.92?m. Both growth and decay characteristics of the optical degradation were investigated. As a class, these fibers represent the most radiation resistant optical waveguides measured to date in the laboratory. Radiation-induced optical losses were in general lower at the longer wavelength but the response of all fibers was extremely nonlinear and complex with an important parameter being previous radiation history. For applications that do not require extremely low loss or ultra-high bandwidth but which demand radiation hardness, these large core PCS fibers must be considered as the most attractive candidates available to the systems' designer.

Radiation-Induced Optical Absorption Spectra of Fiber Optic Waveguides in the 0.4–1.7 μ Region

Abstract: Spectral measurements of the permanent and transient radiation-induced optical absorption in state-of-the-art low loss step and graded index optical fiber waveguides have revealed radiation-induced increases in the OH overtone and combination bands which limit the transmission at long wavelengths. The induced damage in Ge-doped silica core fibers codoped with B has been observed to increase at wavelengths longer than 1.05 μ, and P has been identified as a dopant which suppresses the intense uv Ge-related transient absorption in Ge-doped silica fibers but results in greater permanent damage in the visible and near ir.