Direct Generation Of Femtosecond Vortex Beam From A Yb:Kyw Oscillator Featuring A Defect-Spot Mirror

We have demonstrated the first direct femtosecond vortex beam generation from a semiconductor saturable absorber mirror (SESAM) mode locked Yb:KYW oscillator, featuring a homemade defect-spot mirror. Experimentally, a Laguerre Gaussian LG(01) vortex beam with a repetition rate of similar to 103.5MHz and a pulse duration of 298 fs has been obtained. Both the defect mirror induced spatial loss modulation and intra-cavity astigmatism are responsible for the doughnut mode generation. Further, the chirality of the vortex beam is controlled by slightly tilting the angle of the Yb: KYW crystal, which hence breaks the azimuthal symmetry inside the laser cavity and leads to differential losses for LG(0,+1) and LG(0,-1) modes. The potential of the vortex beam's amplification by a 2-m long Yb-doped double cladding fiber (DCF) amplifier has also been demonstrated. (C) 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement