Wavelength-tunable ultrafast vortex Yb:KGW laser

Wavelength and orbital angular momentum (OAM) are two significant parameters to enhance the capacity and spectral efficiency of the communication system. In this paper, by combining the wavelength tunability, OAM and mode locking technique, we report wavelength-tunable picosecond and femtosecond vortex lasers, which are achieved by defect spot mirror and different thicknesses of birefringent filter as wavelength selective elements. CW vortex laser with 34 nm tuning range, picosecond vortex laser with 11 nm and femtosecond vortex laser with 4 nm are obtained in the experiment. The mode-locked pulses of the vortex laser is as short as 756 fs by using 0.5 mm thick BF and 1.78 ps by using 2 mm thick BF. The maximum output powers are 468 and 482 mW respectively. The maximum pulse energy is 4 nJ. Comparison of pulse duration between LG mode and TEM00 mode indicates that of LG mode is larger TEM00 mode, due to the decrease of phase velocities and increase of mode dispersion. Such wavelength-tunable ultrafast lasers can be used in medical treatment, multi-channel optical communication and quantum entanglement.