Materials for high-power fiber lasers

The absorption and emission properties of silica based ytterbium doped preforms, made by Modified Chemical Vapor Deposition, and of the drawn fibers were investigated as a function of the atmosphere during the preform collapsing. Under increasingly reducing conditions for the collapsing atmosphere, a strong UV/VIS absorption is built up, accompanied with an UV excited emission in the visible region, obviously induced by the formation of Yb²⁺ ions. Both the fluorescence lifetime of the Yb³⁺ lasing level and the cooperative fluorescence in the visible are remarkably diminished. Laser power experiments with the different fibers show a strong deterioration of the laser efficiency parallel to the degree of reduction of the doped glasses.