Jacqueline A. Ruller

The effect of gamma-irradiation on the density of various types of silica

Abstract The radiation-induced changes in density of 11 different silicas, both natural and synthetic, exposed to gamma-irradiation from 10 4 –10 9 rad were measured using a linear density gradient column. It was determined that, in general, the ‘dry’ silicas that contain less than 150 ppm OH compact monotonically with dose; however, the silicas containing more than 150 ppm OH tend to expand initially and then compact at higher doses.

Excitonic optical nonlinearity in quantum‐confined CuCl‐doped borosilicate glass

The nonlinear refractive index n2 is reported for quantum‐confined CuCl microcrystallites in borosilicate glass near the Z3 excitonic resonance. Induced index changes were estimated using Kramers–Kronig analyses of absorption bleaching data from 370 to 388 nm. The nonlinearity was found to increase with increasing particle radius over the range 22 to 34 A, in agreement with theoretical predictions.

Raman and infrared spectra of lead gallosilicate glasses

Abstract Infrared and Raman spectra for two series of lead gallosilicate glasses were measured. Vibrational spectra are fully consistent with a previous structural model for these glasses consisting of two ‘sub’-networks of polyhedral chains, i.e., a gallium tetrahedral network and a lead pyramidal network, intertwined in various configurations. Silica enters the glass substituting directly for GaO 4 tetrahedra in the gallium sub-network. Vibrational bands associated with the bonds necessary to form this type of structure are present in both infrared and Raman spectra. Discrete sub-networks are indicated by the presence of separate bands attributable to both GaOGa bonds and PbO bonds (contained within lead chains). The intensities and frequencies of these bands as well as those attributable to intra-network bonds vary with composition in a manner predicted by the structural model. The SiO vibration frequency is close to that reported elsewhere for the vibrational band associated with SiOGa bridges.

Permanent photowritten optical gratings in irradiated silicate glasses.

We show that permanent optical gratings can be photowritten into simple silicate glasses by exposure to interfering beams of an Ar-ion laser after the glass has been treated by x rays. Gratings with index modulations as large as Deltan = 10(-5) can be formed in less than a minute by exposure to write beams with intensities of the order of 50 W/cm(2).

A structural model for PbOGa2O3SiO2 glasses

Abstract The effect of composition on the glass transformation temperature, viscosity, coefficient of thermal expansion, and density/molar volume of PbOGa2O3SiO2 glasses was investigated. Trends in these data cannot be fully accounted for by previous structural explanations of the properties and glass-forming ability of the PbOGa2O3-based heavy metal oxide glasses. A new structural model is proposed which incorporates what is known about the structures of both PbOSiO2 and PbOGa2O3 glasses to explain the anomalies in composition-property relationships demonstrated in this paper. In addition, this model is able to account for the discontinuities in the properties of PbOGa2O3 binary glasses which occur near the 75PbO25Ga2O3 composition.

Permanent Photoinduced Refractive Index Changes in Rare Earth Doped Glasses

Permanent refractive index gratings were holographically photowritten into rare earth doped glasses using the 488 rn line of a Ar Ion laser. The rare earths Pr 3+ , Tb 3+ , and Eu 2+ were examined. Experiments were performed to elucidate the mechanism responsible for the photoinduced index change. A model is presented in which the index change is accomplished through photoionization of the rare earth dopant and subsequent trapping of the free carrier. The viability of these materials for use in optical fiber grating devices is discussed.

Finite element analysis of deformation in large optics due to space environment radiation

Dose gradients in large mirror substrates due to unequal exposure to the natural space radiation environment have been calculated for two circular orbits: 1200 km altitude/98 deg inclination and 3700 km/30 deg. Dose gradients were translated to density-change profiles based on experimentally determined density changes as a function of dose for fused silica and the low-CTE glass ceramic, Zerodur-M. Finite element analysis of deformation due to the radiation-induced density gradient was performed for a 4 meter by 0.5 cm disk representing a mirror faceplate. Displacements of nearly 2500 micrometers at the outer edge were calculated for a Zerodur faceplate after 10 yr at 3700 km/30 deg. Silica, which is much less sensitive, deformed by only a few angstroms. Reinforcement with a backing having the equivalent stiffness of 5 cm of SiC resulted in a 10-fold decrease in the calculated deformation.

PHOTOSENSITIVITY OF RARE EARTH-DOPED GLASSES

Rare earth-doped glasses exhibit high initial photosensitivity but their response saturates at relatively modest values of (Delta) n (approximately 5 X 10-7), which greatly limits their usefulness for device applications. In the context of our model, saturation results from either exhaustion of photosensitive rare earth sites, trap sites, or through competition between two photon creation and one photon bleaching processes. In this paper we report the results of new experiments designed to further elucidate the photosensitivity process with specific emphasis on the saturation mechanisms(s). Based on these new experimental results we present a refinement of our earlier model.

Nonlinear optical susceptibility of CuCl quantum dot glass

The third order optical nonlinearity of quantum confined CuCl-doped borosilicate glass caused by saturation of the excitonic absorption is reported. Induced index changes were estimated using the Kramers-Kronig analysis of the bleaching data. The nonlinear refractive index is reported as a function of particle radius and is found to increase with increasing radius over the range 22 A to 34 A.