Efficient laser operation with nearly diffraction-limited output from a diode-pumped heavily Nd-doped multimode fiber

Laser performance of a diode-pumped Nd-doped multimode phosphate-glass fiber is reported. The selection of the fundamental mode in a multimode fiber is demonstrated, resulting in laser emission that is close to diffraction limited and that is nearly independent of the pump power. The heavily Nd-doped fibers with core diameters of 100 microm and lengths between 13 and 32 mm deliver as much as 130 mW of cw output power at 1.053 microm. A total efficiency of 31% with respect to launched pump power has been achieved.