Abstract

Ytterbium-doped femtosecond fiber amplifiers appear as a promising alternative technique compared to bulk systems, in particular in terms of efficiency and average power handling. However, for high energy systems, the available gain bandwidth of ytterbium limits the achievable pulsewidth through gain narrowing (GN) to 300 fs for pulse energies of tens of μJ [1]. We have recently investigated a nonlinear chirped-pulse amplification regime where mild stretching causes the self-phase modulation (SPM) to generate significant spectral content, thereby compensating GN [2]. Here we use this idea on two amplification stages, i.e. the stretching ratios are adapted to the amount of gain narrowing experienced in each stage. This leads to a system where nonlinearity is managed and distributed over the amplification stages in order to maintain the pulse bandwidth, while minimizing the detrimental impact of accumulated nonlinear phase on the compressed pulse quality. We demonstrate the generation of high temporal quality 20 μJ 202 fs pulses at a repetition rate of 200 kHz.

© 2009 IEEE