Transfer of orbital angular momentum from a super-continuum, white-light beam.

Beams with helical phasefronts described by exp(ilphi) carry an orbital angular momentum equivalent to lh per photon. Using diffractive optics this helical phase structure can be applied to every spectral component of the beam such that a spatially coherent white-light beam can carry orbital angular momentum without any chromatic distortion. This achromatic property can be hard to achieve in spin angular momentum where pure circular polarization is difficult to maintain across a finite spectral bandwidth. We illustrate the achromatic, helical phase structure of a white-light beam by observing the transfer of its orbital angular momentum to particles held in optical tweezers.