272 W quasi-single-mode picosecond pulse laser of ytterbium-doped large-mode-area photonic crystal fiber

A large-mode-area ( LMA) ytterbium-doped photonic crystal fiber ( PCF) with core NA of 0.034 and core diameter of 50 mu m 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 x 10(-4) compared with pure silica was prepared by the sol-gel method and heat homogenization at 2000 degrees 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 M-2 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.