100 fs pulses directly from a kW-class mJ-level ytterbium-doped fiber CPA laser system
We present a large-bandwidth high-power, high-energy fiber laser system based on coherent beam combination of 16 ytterbium-doped rod-type amplifiers. The CPA pulse stretching as well as extensive spectral shaping to counteract gain narrowing are implemented in a mostly fiber-integrated front end. A two-staged and partially helium-filled CPA grating compressor allows to compress the amplified pulses while maintaining a nearly diffraction-limited beam quality. Two laser operation regimes were investigated. The first one aimed for the shortest possible pulse duration, whereby 106 fs were reached at an average power of 910 W and a pulse energy of 910 µJ. In a second experiment, the primary aim of increasing the average power to 1 kW and the pulse energy to 10 mJ was successfully reached while the secondary objective, again being a minimum pulse duration, was optimized to 120 fs, posing a record value for fiber-CPA systems at this performance level.