We explored high-energy and high-peak-power pulse generation in large-core multimode fiber amplifiers, achieving what is to our knowledge the highest reported energies, up to 82 mJ for 500-ns pulses, 27 mJ for 50-ns pulses, and 2.4-MW peak power for 4-ns pulses at 1064 nm, using 200-µm-diameter and 0.062-N.A. core Yb-doped double-clad fiber amplifiers. The highly multimode nature of the fiber core was mitigated by use of a coiling-induced mode-filtering effect to yield a significant improvement in output-beam quality from M^2 = 25 from an uncoiled fiber to M^2 = 6.5 from a properly coiled fiber, with the corresponding reduction in number of propagating transverse modes from >or=200 to <or=20.
© 2005 Optical Society of America
Ming-Yuan Cheng, Yu-Chung Chang, Almantas Galvanauskas, Pri Mamidipudi, Rupak Changkakoti, and Peter Gatchell, "High-energy and high-peak-power nanosecond pulse generation with beam quality control in 200-µm core highly multimode Yb-doped fiberamplifiers," Opt. Lett. 30, 358-360 (2005)