Codoped materials for high power fiber lasers: diffusion behaviour and optical properties

Optical fibers for high power lasers and amplifiers are fabricated on the basis of quartz glass which has outstanding properties concerning high fiber strength, high power hardness and low optical losses compared with other glasses such as heavy metal fluoride or oxide glasses. It is well known, however, that the host properties of pure silica regarding the active rare earth ions are insufficient and the laser medium has to be improved by the incorporation of codopants. Here we present new investigations of material and fiber properties for phosphorus/aluminium codoping, with regard to the realization of efficient rare earth doped cw and pulsed high power fiber devices. The diffusion behaviour in the complex systems shows characteristic interaction effects, which influence the dopant concentration and their spatial distribution. The refractive index in the codoped systems and the basic attenuation deviate remarkably from additivity relations. The absorption spectrum in the VIS/NIR region depends on codopant concentration and on preparation conditions, with influence on the fluorescence properties of the rare earths and the laser efficiency.