Determination of the radiation response of doped-fiber laser materials, systems and components to relevant ionizing radiation fluxes is central to the prediction of long-term fiber-based laser performance/survivability in adverse and/or space-based environments. It is well known that optical elements that are placed into orbit around the Earth experience harsh radiation environments that originate from trapped-particle belts, cosmic rays, and solar events. Of particular interest to optical materials is the continuous flux of gamma photons that the materials encounter. Such radiation exposure commonly leads to the formation of color centers in a broad range of optical materials. Such color center formation gives rise to changes in optical transmission, loss and luminescent band structure, and, thus, impacts long-term optical device performance.In this paper we will present the results of our investigation of gamma-radiation-induced photodarkening on the passive optical transmittance of a number of ytterbium-(Yb-) doped optical fibers. We will discuss the evolution of the optical response of the fiber across the 1.0 to 1.6 micron wavelength window with increasing gamma exposure. Results indicate that these fibers exhibit reasonable radiation resistance to gamma exposures typical of a 5-year, low-earth-orbit environment. Maximum transmittance losses of less than 10% were observed for total gamma exposures of 2-5 krad (Si).

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Theoretical calculations based on time-dependent density functional theory are used to characterize the electronic absorption spectrum of a heteroleptic Ti-alkoxide molecule, (OPy)(2)Ti(TAP)(2) [OPy = pyridine carbinoxide, TAP = 2,4,6 tris(dimethylamino)phenoxide] under investigation as a photosensitive precursor for use in optically initiated solution synthesis of the metal oxide. Computational results support the assignment of UV absorption features observed in solid-state precursor films to key intrinsic ground-state transitions that involve ligand-to-metal charge transfer and pi-pi* transitions within the cyclic ligand moieties present. The nature of electron density redistribution associated with these transitions provides early insight into the excitation wavelength dependence of photostructural modification previously observed in this precursor system.