High-power, high repetition rate, tunable, ultrafast vortex beam in the near-infrared

We report on experimental demonstration of high power, ultrafast, high repetition rate (RR) vortex beam source tunable in the near-IR wavelength range. Based on single-pass optical parametric generation of Yb-fiber laser of vortex order l(p) = 1 in a 50 mm long MgO doped periodically poled LiNbO3 crystal, the source produces signal beam in vortex profile of order l(s) = 1 across 1433-1553 nm. Additionally, the source produces broadband idler radiation tunable across 3379-4132 nm in the Gaussian beam profile. We observed that the vortex profile of the pump beam is always transferred to the signal beam due to the highest overlapping integral among the interacting beams and the idler maintains a Gaussian spatial profile owing to the conservation of orbital angular momentum in optical parametric processes. For a pump power of 4.72 W, the signal and idler beams have a maximum power of 1.7W at 1509 nm and 0.48W at 3625 nm respectively. The signal vortex beam has output pulses of width similar to 637 fs at a RR of 78 MHz. The signal (idler) has a spectral width of 4.3 nm (129.5 nm) and a passive peak-to-peak power fluctuation better than 3% (1.1%) over 30 min, respectively.