  We show how the effects of azimuthal optical aberrations on singular light
beams can result in an intensity modulation in the beam waist or focal point
spread function (PSF) that is directly proportional to the amplitude of the
applied phase aberration. The resulting distortions are enough to significantly
degrade the utility of the singular beams even in well corrected optical
systems. However we show that pattern of these intensity modulations is related
to the azimuthal order of the applied aberration and we suggest how this can be
used to measure those aberrations. We demonstrate a closed loop system using a
liquid crystal spatial light modulator as a programmable diffractive optical
element to both generate the beam and correct for the sensed aberrations based
on feedback from a CCD detected intensity image of the focal point spread
function.
