Investigation of Nd:Yb - codoped silica fibers as a laser material
The increasing interest in high power fiber lasers is connected with the task of providing the necessary pump energy at acceptable costs. High power laser experiments with commercially available multi-wavelengths diode laser systems and silica fibers codoped with Neodymium (Nd) and Ytterbium (Yb) demonstrated the potential of this laser concept. Fluorescence investigations of Nd:Yb-codoped silica fibers proved an effective energy transfer from stimulated Nd ions to Yb ions. To get a better understanding of this laser medium we investigated the fluorescence spectra, the fluorescence decay and the laser characteristics both experimentally and theoretically. In conclusion, we present experimental results and a model for the understanding of fluorescence and laser properties of Nd:Yb-codoped silica fibers
Spectroscopy of Nd3+ and Yb3+ codoped fluoroindogallate glasses
The Nd–Nd and Nd–Yb energy transfer processes are studied in lead fluoroindogallate glasses with the following molar composition: 30PbF2–20GaF3–15InF3–15ZnF2–(20–X)CaF2–XNdF3 (with X=0.1, 0.5, 1, 2, 4, and 5), 30PbF2–20GaF3–15InF3–15ZnF2–(20–X)CaF2–XYbF3 (with X=0.1, 0.5, 1, 2, 3, and 5), and 30PbF2–20GaF3–15InF3–15ZnF2–(19–X)CaF2–XYbF3–1NdF3 (with X=0.1, 0.5, 1, 2, 3, and 5.5). The Dexter, Yokota–Tanimoto, and Holstein formalisms were used to treat the experimental data. The following microparameters of energy transfer were obtained: CDD(Nd–Nd)≈7×10−40, CDA(Nd–Nd)=2.5×10−40, and CDA(Nd–Yb)≈3×10−40 cm6/s. It was also shown that the energy migration between Nd ions depends on the third power of temperature (T3) up to a saturation value of about 80 K. This behavior was attributed to the site to site energy migration. The Yb doped samples presented no nonradiative losses for the Yb3+ emission at 969 nm.
A preliminary account of a new tyrannosauroid theropod from the Wessex Formation (Early Cretaceous) of southern England
Abstract A new genus and species of coelurosaurian theropod dinosaur from the Wessex Formation (Early Cretaceous, Barremian) of the Isle of Wight, England, is described and named. Distinctive characters of the premaxilla, its dentition, maxilla and nasals allow it to be diagnosed. The teeth in the premaxilla are D-shaped in cross-section and the nasals are fused. The hands are elongate and slender and the hindlimbs are gracile. Lack of element fusion elsewhere in the skeleton suggests that it is a subadult. Numerous character states are shared with tyrannosaurids but the new taxon appears to be excluded from the group that comprises aublysodontine and tyrannosaurine tyrannosaurids. We conclude that the taxon is a basal tyrannosauroid and as such it is one of the earliest and (with the exception of some teeth and an isolated ilium from Portugal) the first from Europe. Implications for tyrannosauroid biogeography and evolution are discussed. The animal was part of an unusual taphonomic assemblage in which some elements were partially articulated while others were scattered or broken.