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.
Mathematical Modeling of Scour and Deposition
Electronic computers are opening up the field of sedimentation engineering by permitting the analysis of problems which heretofore have required too much time and effort. Movable stream bed profiles are being calculated in addition to water surface profiles. The initial gradation of sediment material in the stream bed may be prescribed to facilitate the calculation of an armor layer. This gradation is continually changed by the computer program in response to sediment particles being deposited on the stream bed and material on the stream bed being removed to satisfy transport capacity. Hydraulic sorting of sediment by grain size is accomodated. The stream bed does not have to be represented by a single grain size. Retardance of motion because of armor layer is calculated.