The generation of femtosecond optical vortex beams with megawatt powers directly from a fiber based Mamyshev oscillator

Abstract: Numerous approaches have been developed to generate optical vortex beams carrying orbital angular momentum (OAM) over the past decades, but the direct intracavity generation of such beams with practical output powers in the femtosecond regime still remains a challenge. Here we propose and experimentally demonstrate the efficient generation of high-peak-power femtosecond optical vortex pulses from a Mamyshev oscillator (MO) based on few-mode polarization-maintaining (PM) ytterbium-doped fibers (YDFs). By employing an appropriate intracavity transverse spatial mode selection technique, ultrafast pulses carrying OAM with selectable topological charge of l = ±1 are successfully generated with an average output power of ~5.72 W at ~24.35 MHz repetition rate, corresponding to a single pulse energy of ~235 nJ. The chirped pulses can be compressed to ~76 fs outside the cavity, leading to a pulse peak power of ~2.2 MW. To the best of our knowledge, this is by far the highest pulse energy and peak power for optical vortex pulses ever generated directly from a fiber oscillator. This unprecedented level of performance should be of great interest for a variety of applications including materials processing and imaging.