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23 fs pulses at 250 W of average power from a FCPA with solid core nonlinear compression

We report on a linear polarized high power femtosecond fiber chirped-pulse amplification (FCPA) system operating at 360 W of average power with an excellent beam quality (M2=1.2). A mode locked fiber oscillator with a repetition rate of 250 MHz seeds the FCPA system. The 265 fs pulses are shortened in time employing the nonlinear compression technique. An unprecedented combination of average power, pulse duration and repetition rate is reached with an excellent beam quality by using a solid-core photonic-crystal fiber nonlinear compression stage. Thereby, the peak power of the fiber chirped pulsed amplification system is close to the self-focusing threshold of fused silica (case of linear polarization). In order to avoid self-focusing the threshold is increased by changing the polarization from linear to circular. Finally, the second order dispersion is compensated with a chirped-mirror compressor reaching shorter pulse durations. We achieve pulse shortening by more than one order of magnitude down to 23 fs pulses, compressed pulse energy of 0.9 μJ and a peak power of 34 MW at an average power level of 250 W. At this power level we measure an excellent beam quality (M2=1.3). This system is an ideal laser source for studying high field physics, e. g. driving enhanced cavities for high-repetition-rate high-harmonic generation.