Femtosecond vortices generated from a self-started Kerr-lens mode-locked Hermite-Gaussian thin-disk oscillator with a defective mirror.

We demonstrate the generation of stable femtosecond vortices from a self-started Kerr-lens mode-locked Yb:YAG thin-disk oscillator. By using a defective mirror inscribed with a fine line, 218-fs Hermite-Gaussian (HG) pulses are delivered directly from the thin-disk oscillator with an average power of 12 W at the repetition rate of 105 MHz and subsequently converted to Laguerre-Gaussian (LG) vortices by a cylindrical-lens mode-converter. The average output power of the Hermite-Gaussian pulses is further improved to 19 W by applying a rectangular aperture. This is the highest, to the best of our knowledge, average power obtained from any mode-locked Hermite-Gaussian oscillator to date. This work provides an effective way to generating a high-order and high-power ultrafast vortex beam.