Demonstration of spatial distribution of photodarkening in yb-doped large-mode-area fibre laser

Yb-doped silica fibres are used in lasers and amplifiers at the 1.0-1.1 mum wavelength range. Large-mode-area fibres are preferred in applications requiring high output peak powers, and are often coiled to improve beam quality. Photodarkening is a detrimental effect that under some conditions can decrease the transmittance of the Yb-doped core of the fibre, causing output power degradation. The spatial distribution of photodarkening in coiled large-mode-area fibres that are used as CW fibre laser cavities are experimentally demonstrated. Simulation results describing and supporting the results are presented.