The ELI-ALPS facility requests lasers with parameters beyond current state-of-the-art . One of the most challenging ones is the high repetition rate laser 2 (HR2), a carrier-envelope-phase stable laser system delivering 5mJ pulses at 100kHz repetition rate and with pulse durations of 6fs, which is currently under development at Active Fiber Systems GmbH. It uses a kW-class ytterbium doped femtosecond fiber-chirped-pulse amplifier system. To achieve the bandwidth required for few-cycle pulses significant nonlinear spectral broadening is necessary. The latter technology has seen rapid scaling both in terms of average power  and pulse energy [3,4]. Furthermore, by the introduction of stretched hollow capillaries  high-quality long waveguides became available, which is inevitable for upscaling the pulse energy. Despite first promising experiments with ytterbium-based laser systems the average power used in combination with stretched-hollow-core fibers has not exceeded a few Watt yet [6,7].
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