Tunable mode-locked fiber laser to generate ultrashort cylindrical vector beams

In this work, we report a tunable mode-locked fiber laser that can produce ultrashort laser pulses with polarization vortex. Two vortex wave plates (VWPs) are employed in this laser to convert the intracavity beam states between the Gaussian mode and cylindrical vector mode. By adjusting the angle between a diffraction grating and the light beam in the cavity, the center wavelength of the mode-locked pulse can be tuned from 1015 nm to 1030 nm. Mode-locked pulses with full width at half maximum of 1.51 ps with the maximum single pulse energy of 2.2 nJ have been obtained. Through synchronously adjusting the orientations of the two VWPs, the output mode can be switched between radial polarization and azimuthal polarization states. The output vortex pulse from the tunable mode-locked fiber laser may find many applications such as optical manipulation, imaging and laser micro-machining.