Abstract
A two-stage fiber-based femtosecond amplification system is presented, based on chirped-pulse amplification in highly nonlinear regime. The amount of self-phase modulation is separately adjusted in each stage selecting the proper stretching ratio in order to compensate gain narrowing. Analytical design rules are validated using numerical simulations. Our experimental implementation leads to the generation of high temporal quality 20 microJ 202 fs pulses at repetition rate of 200 kHz, a record duration at this energy level.
Highlights
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
The amount of self-phase modulation is separately adjusted in each stage selecting the proper stretching ratio in order to compensate gain narrowing
Our experimental implementation leads to the generation of high temporal quality 20 μJ 202 fs pulses at repetition rate of 200 kHz, a record duration at this energy level
Summary
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. Harmful nonlinear effects and damage thresholds are reached sooner than in bulk amplifiers because the mode-field area in the fiber is limited in order to retain a good beam quality, and the interaction length with the medium is large. Another limitation of fiber amplifiers is the achievable pulse duration. It was until recently limited to stretcher-free setups, in the framework of the self-similar or parabolic propagation regime [7] This concept has been used with current large mode area (LMA) fibers to generate output pulse energies around 1 μJ with a pulsewidth of 70 fs, but the energy cannot be further scaled due to damage and self-focusing thresholds. We demonstrate the generation of high temporal quality 20 μJ 202 fs pulses at a repetition rate of 200 kHz
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