A large-mode-area (LMA) ytterbium-doped photonic crystal fiber (PCF) with core NA of 0.034 and core diameter of 50 μm was made by the stack-and-draw technique. The core is formed by Yb³⁺/Al³⁺/F /P⁵⁺ co-doped silica glass containing 0.09 mol% Yb₂O₃ with an absorption coefficient at 976 nm up to 3.2 dB/m. The core glass with homogeneous distribution of Yb³⁺ ions and refractive index difference of 4 × 10 ⁴ compared with pure silica was prepared by the sol-gel method and heat homogenization at 2000°C. Laser power amplification of this LMA PCF was studied using a seed source of 21 ps pulse duration and 48.7 MHz repetition rate at 1030 nm wavelength. With pump power of 520 W, a maximum 272 W (266 kW peak power) quasi-single-mode laser output with M² of 2.2 was achieved in a 4.7 m fiber length bent at a diameter of 47 cm with slope efficiency of 52%, and no obvious mode instability, stimulated Raman scattering, or thermal damage on the end facet of the fiber were observed.

We produce a maximum 1.45 W laser output at 1064 nm using a neodymium-doped silicate glass fiber that has a rectangular core with dimensions of ～6.3 μm×31.5 μm. The measured divergence angles of the output laser in two dimensions are 3.22° and 1.76°, respectively. The output power is stable and limited only by the available pump power.