Pump propagation and absorption in active tapered double-clad fiber has been analyzed based on a ray optics approach. Optimization of the longitudinal shape, absorption and angular distribution of the pump beam allowed for power scaling of a ytterbium fiber laser up to 600 W with high beam quality (M2≤1.08) and a slope efficiency of 63%. It is shown that the influence of vignetting in a tapered fiber can be avoided, resulting in high overall efficiency, in good agreement with the presented model.
© 2009 Optical Society of America
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