Femtosecond optical vortices open a variety of applications, ranging from femtosecond micro-processing to vortex strong-field physics. Thus far, the generation of high-order femtosecond vortices remains a challenge. The 1st to 4th order tunable femtosecond vortices generated by a z-type cavity semiconductor saturable absorber mirror mode-locked Yb:CALGO laser are reported in this study. The anti-reflection coated Yb:CALGO crystal is used as the gain material and is positioned perpendicular to the laser beam to avoid an angle dispersion, which results in multi-transverse-mode running. The astigmatism caused by the tilted curved mirrors is compensated by elevating the folding mirrors adjacent to the curved mirrors. The 1st to 5th order tunable femtosecond Hermite-Gaussian (HG n0 ) modes are realized by employing the off-axis pumping technique. The mode-locked pulse width is in the range of 220-580 fs for various HG modes. The mode-locked HG modes are converted into femtosecond vortices using a cylindrical-lens mode converter. The work provides a reliable way to generate high-order femtosecond vortex beams.

Ultrafast vortex pulses emitted at 1 μm band are highly sought after in many fields, here we propose an all-fiber laser for achieving that. The designed laser is switchable to emit ultrafast orbital angular momentum (OAM) and cylindrical vector beams. The beam purities are calculated to be higher than 94%. Moreover, the as-designed laser can achieve ultrafast pulse with a duration of 10.4 ps and maximum energy of 619.3 pJ. Generally, it is the shortest width and largest energy of OAM emission in ultrafast ytterbium-doped all-fiber laser so far.

Flat-top beams have plenty of applications in theoretical and applied research, but they are not eigenmodes of the wave equation. Here, we propose an effective strategy for generating flat-top beams in fibers, which originates from the incoherent superposition of orbital angular momentum (OAM) and fundamental (LP01) modes. The designed all-fiber passively Q-switched laser can realize high-quality pulsed flat-top and OAM beam emissions. The normalized root mean square of the flat-top beam is around 4.7%, and the purity of the OAM mode is calculated to be higher than 98%. For the first time to the best of our knowledge, pulsed emission of a flat-top beam is achieved using an all-fiber laser. Moreover, its repetition rate and duration can be controlled by adjusting the pump.

We report on a wavelength and duration tunable mode-locked Yb-doped fibre laser operating in a dissipative soliton resonance (DSR) regime at a sub-megahertz repetition rate. The DSR regime has the advantage of avoiding pulse splitting. Hence, it is suitable for obtaining a high output pulse energy. In the experiment, by extending the cavity length to 219.36 meters, a DSR pulse output with a repetition rate of 923 kHz is achieved. For the case of the DSR operating at 1032 nm, the maximum single-pulse energy is 113 nJ. The output pulse duration can be changed from 389 ps to 1.25 ns by controlling the pump power. A wavelength-tuned range of 73 nm (1007-1080 nm) is further realized by adjusting the intra-cavity spectral filter.

Vortex beams have wide applications in optical tweezers, optical communications and so on. Long period fiber gratings, mode selective couplers, few mode fiber Bragg gratings or specially designed fibers are often used to generate vortex beams from fiber lasers. New methods of mode selection in fiber lasers are always attractive. When transverse modes propagate along a multimode fiber, the polarization state of each mode rotates differently due to birefringence. In this paper, a linear cavity fiber laser and a ring cavity fiber laser using a polarization rotation technique are proposed to select the output laser mode. Three waveplates and a polarizing beam splitter (PBS) are used as a mode loss controller inside the laser cavity. By rotating the waveplates inside the cavity, different laser modes can be selected and achieved from the laser cavity by the PBS. Experimentally, the fundamental LP01 mode, the LP11 mode, the LP21 mode and vortex beams with ±1 topological charges were achieved.