The dispersive Fourier transform technique provides feasibility of exploring non-repetitive events and the buildup process in ultrafast lasers. In this paper, we report a new buildup process of dissipative solitons in a simplified mode-locked Yb-doped fiber laser, which includes more complex physics stages such as the Q-switching stage, raised and damped relaxation oscillation stages, noise-like stage, successive soliton explosions stage, and soliton breathing stage. Complete evolution dynamics of noise-like pulse and double pulse are also investigated with dispersive Fourier transform. For the noise-like pulse dynamics process, it will only experience the Q-switching and relaxation oscillation stages. In the case of dissipative soliton and noise-like pulse, the double pulse buildup behavior is manifested as the replication of individual pulses. A weak energy migration occurs between two pulses before reaching steady state. Meanwhile, real-time mutual conversion of the dissipative soliton and noise-like pulse has been experimentally observed, which appears to be instantaneous without extra physical processes. To the best of our knowledge, this is the first report on these physical phenomena observed together in a mode-locked fiber laser. The results further enrich the dynamics of mode-locked fiber lasers and provide potential conditions for obtaining intelligent mode-locked lasers with controllable output.

Noise-like pulses having a pedestal of 690 fs and a spike of 59.6 fs were generated in a nonlinear Yb-doped fiber amplification system. The seed source is a mode-locked Yb-doped fiber laser by nonlinear polarization rotation, and dissipative soliton pulses were obtained in it. Then, the dissipative soliton pulses passed through a 7.6 m dispersive fiber to enhance the dispersion and nonlinearity. Further on, the dissipative soliton pulses were launched into a Yb-doped fiber nonlinear amplifier, and stable noise-like pulses with a pedestal of 6.26 ps and a spike of 227 fs were achieved. Finally, by a grating pair, the pedestal and spike of the noise-like pulses were effectively compressed to 690 fs and 59.6 fs, respectively. To the best of our knowledge, this is the shortest pedestal demonstrated in noise-like pulses operating at 1 μm.

Few-layer graphitic carbon nitride (g-C₃N₄) nanosheets were fabricated and utilized as a saturable absorber for mode-locking in an Er-doped fiber laser with net normal dispersion. The g-C₃N₄/polyvinyl alcohol (PVA) hybrid-film-based saturable absorber has a modulation depth of 4.01% and a saturation intensity of 7.5 MW/cm². By integrating g-C₃N₄-PVA mode-locker into the laser cavity, a mode-locked operation could be obtained. The achieved mode-locking pulse centered at 1530.3 nm has a pulse width of 530 ps. Its repetition rate is 40.8 MHz, and the corresponding signal-to-noise ratio is about 55 dB.

We experimentally demonstrate a cascaded Raman scattering continuum, utilizing a compact mode-locked Yb-doped fiber laser based on a nonlinear polarization rotation technique in the all normal dispersion regime. There is no physical filter or polarization controller in the oscillator, and a different mode-locked operation is achieved, corresponding to the extra fiber location in the oscillator. The broadband spectrum generation owes to the enhanced stimulated Raman scattering progress. The maximum output average power and peak power are 14.75 nJ and 18.0 W, and the short coherence light is suited for optical coherence tomography.

Self-Q-switching is observed in a bulk Yb:KGd(WO4)2 oscillator without any additional modulating elements. The output power reaches 434.4 mW at a pump power of 13.67 W, corresponding to pulse repetition rate of 125 kHz and a pulse duration of 2.5 μs, respectively. The mechanism of self-pulse formation is explained by the re-absorption effect of the Yb3+ ion in Yb:KGd(WO4)2.