Microjoule-level picosecond and femtosecond mode-locked fiber oscillators

This study demonstrates femtosecond mode-locked fiber oscillators that can generate pulse energies beyond the microjoule-level at high average power. In the experiment, an endlessly single-mode passive fiber-based mode filter is applied inside the cavity, resulting in an M² value of about 1.2 at the output. In the femtosecond regime, the saturable absorber mirror with high modulation depth (~30 %) and fast relaxation time (~500 fs) is employed, which produces a cavity repetition rate of about 9.7 MHz. In the single pulse regime, the highest possible average output power is as high as 9 W, corresponding to a pulse energy of 927 nJ. The step edges shape emission spectrum is shown, along with the 1034.6 nm center wavelength and the 8.8 nm spectral bandwidth. The fiber laser generates positively chirped 8 ps-long output pulses, which are then compressed down to 711 fs with up to megawatt peak power levels.