  We describe an optical beam converter for an efficient transformation of
Gaussian femtosecond laser beams to single- or double-charge vortex beams
showing no spatial or topological charge dispersion. 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.
