39-mW annular excitation of ytterbium fiber laser with radial polarization

An efficient radial-polarization Yb-fiber laser with an intracavity Brewster axicon is demonstrated. The fraction of ASE at low pumping and parasitical oscillation are minimized by adopting bidirectional pumping and angle-polished fiber end. So far, except for the improvement in polarization purity and cylindrical symmetry of output beam, 39-mW output power is obtained at 460-mW launched pump power with 13.8% slope efficiency. And also a new type of low-V-parameter multi-mode gain fiber with doughnut concentration distribution of active ions in fiber core profile is predicted to be promising in improving the laser performance further.