Focusing properties of high charge number vortex laser beams

We investigate experimentally and numerically the propagation characteristics of laser beams formed by imparting an azimuthal phase l phi to a Gaussian beam, where l is an integer. We find that when high-l beams of a finite extent are focused through a lens, the beams achieve peak intensity and are most sharply defined before and after the focal plane. Additionally, in these regions of highest intensity the effect of aberrations on the beam quality is greatly reduced, which we also demonstrate experimentally and numerically. We present a simple geometrical picture that provides excellent estimates of the beam radius and propagation distance to the plane of peak intensity. (C) 2007 Optical Society of America.