Preparation And Research On Radiation Hardened Active Silicate Glasses And Fibers

Active optical fibers have found many applications in fiber-based laser and amplifier systems. Such systems offer the advantages of high efficiency, low waste-heat generation, diffraction-limited beam quality, and ruggedness. These advantages make them appropriate for use in harsh radiation environments, and their low weight and small volume furthermore render them ideal for space-based applications such as space optical communications and space exploration. However, it is clear that radiation exposure leads to the excitation of electrons and the subsequent formation of color centers in the materials. This radiation-induced darkening effect negatively impacts fiber performance.In this dissertation, the effects of gamma-ray radiation on the optical properties of active silicate glasses and fibers were investigated. The radiation-induced absorption band can be suppressed by introducing Ce ions into glass matrix, resulting in a greatly improvement in the radiation resistance of all samples. Main achieved results are listed as follow:(1) Radiation-induced photodarkening caused a strong broad optical absorption band, which had a maximum wavelength centered around400nm and the tail extended into the near infrared region. In addition, a minor part of the Yb3+ions were converted into Yb2+by trapping free electrons during irradiation.(2) The excitation energy could be transfered from Er3+or Yb3+ions to radiation induced defects through upconversion or multiphoton absorption processes under980nm LD pumping. Such energy transfer processes result in a decrease of the upper state lifetime of Er3+or Yb3+ion. Photobleaching effect was observed in irradiated Yb-doped glasses during the fluorescence measurement at room temperature.(3) The Ce ions in silicate glasses can effectively trap holes and free electrons due to their multivalency, consequently suppressing the radiation-induced absorption band. The absorption bands of Ce ions are located in the UV and middle-infrared regions, far removed from the region where fiber systems are operated.(4) The influence of the Ce-codoping on the radiation resistance of active fibers is evident:whereas the Yb-Ce-codoped fibers exhibited a slope efficiency of about50%, the Ce-free Yb-doped fiber showed almost no amplification at all after irradiation.