Efficient beam converter for the generation of high-power femtosecond vortices.

We describe an optical beam converter for an efficient transformation of Gaussian femtosecond laser beams to single- or double-charge vortex beams. The device achieves a conversion efficiency of 75% for single- and 50% for double-charge vortex beams and can operate with high-energy broad bandwidth pulses. We also show that the topological charge of a femtosecond vortex beam can be determined by analyzing its intensity distribution in the focal area of a cylindrical lens.