Resolving the Buildup Dynamics of Harmonically Mode-Locked Mamyshev Oscillator

The harmonic mode-locking (HML) from the Mamyshev oscillator (MO) can produce laser pulses with tunable repetition rate and high pulse energy, which is crucial for many applications in optical communication, frequency metrology and micromachining. However, experimentally verifying the buildup dynamics of HML in MO remains a significant challenge. Here, the all-fiberized erbium-doped MO has been designed to deliver HML pulse with signal-to-noise ratio exceeding 80 dB experimentally. The starting dynamics of HML in the MO characterized by the time-stretch dispersive Fourier transform technique revealed that the generation of HML is not dominated by the splitting effect of the single pulse but the amplification of the multiple seeding pulses in the oscillator. Unlike the generation of the conventional HML, the transition from external seed pulses to stable HML operation in MO involves five ultrafast phases, including relaxation oscillation, multi-pulses operation, pulse collapse reconstruction, unstable HML, and stable HML state. The numerical simulation results further validate our understanding of the HML mechanisms in MO. The results can deepen the understanding of the HML operation in MO, and may provide an active way to control the transient pulse dynamics in the high-performance ultrafast laser systems.