A B-integral management strategy in discrete single-crystal fibers: towards direct power scaling of femtosecond sources near 2 μm

Abstract We propose a B-integral management strategy for manipulating the nonlinear effects by employing a discrete single-crystal fiber (SCF) configuration, enabling direct amplification of 2-μm femtosecond pulses at high repetition rates without additional pulse picking, stretching and compression. The system delivers an average power of more than 56 W at 75.45 MHz with extremely high extraction efficiency (>55%) and near-diffraction-limited beam quality ( M 2 < 1.2). The dynamic evolution of the optical spectra and temporal properties in the power amplifier reveals that detrimental nonlinear effects are largely suppressed due to the low accumulated nonlinear phase shift in the discrete SCF layout. This straightforward, compact and relatively simple approach is expected to open a new route to the amplification of 2-μm ultrashort pulses at MHz and kHz repetition rates to achieve high average/peak powers, thereby offering exciting prospects for applications in modern nonlinear photonics.