Generation of high-energy femtosecond pulses in multimode-core Yb-fiber chirped-pulse amplification systems

220-fs pulses with energies of similar to 100 muJ have been generated by us e of two different configurations of diode-pumped Yb-fiber chirped-pulse am plification systems. Energy scaling was demonstrated with 25-mum-core diame ter fibers, in which stable diffraction-limited output (M-2 similar to 1.1) was achieved. A two-stage fiber-amplifier system produced average powers o f up to 5.5 W at similar to1-MHz pulse-repetition rate. A double-pass confi guration provided 53-dB gain in a single Yb-fiber amplifier stage, thus eli minating the necessity for multiple amplification stages as well as the nee d for using polarization-preserving fibers. (C) 2001 Optical Society of Ame rica