Megawatt peak power Mamyshev oscillator seeded by sub-nanosecond pulses either at 1064 nm or 1033 nm

High peak power (~MW) femtosecond pulses enable a large variety of applications spanning from multi-photon and time resolved spectroscopy, to terahertz generation, from high precision industrial micro-machining, to supercontinuum or high harmonic generation. Quite recently, a new class of fiber lasers based on the so called Mamyshev architecture, have proved capable of reaching this remarkable peak power level directly from an oscillator. Such lasers rely on offset spectral filters and self-phase modulation to realize the equivalent saturable absorber mechanism that produces very stable train of mode-locked pulses in normal dispersion, readily compressed to femtosecond duration extra-cavity. In this work, we exploited phased-matched degenerate four-wave-mixing (DFWM) in a standard single-mode polarization-maintaining passive fiber, to produce a sub-ns seeding pulse at ~1033 nm starting from the PQS pulse at 1064 nm. This permitted to reliably start a 1-W, sub-60-fs femtosecond MO at both wavelengths. Although the overall performance in terms of output power and pulse duration is comparable in both cases, we show that seeding at 1033 nm provides much higher quality and shorter pulses (46 fs) with minimal satellites. Faster evolution toward the gain-managed nonlinear amplification (GMNA) regime clearly happens when seeding closer to the peak gain of the Yb-doped fiber.