title: Direct measurement of the skew angle of the Poynting vector in a helically phased beam.
abstract: We measure the local skew angle of the Poynting vector within a helically-phased, exp (il phi), beam using a Shack Hartmann wavefront sensor. It is the skew angle of the Poynting vector with respect to the beam axis that gives rise to the orbital angular momentum of a light beam. We confirm that this skew angle is l/kr, corresponding to an orbital angular momentum of l? per photon. Measurement of orbital angular momentum in this way is an alternative to interferometric techniques giving a non-ambiguous result to both the magnitude and sign of l from a single measurement, without any restriction on the optical bandwidth.
authors.forename: Jonathan
authors.initials: J
authors.lastname: Leach
authors.forename: Stephen
authors.initials: S
authors.lastname: Keen
authors.forename: Miles J
authors.initials: MJ
authors.lastname: Padgett
authors.forename: Christopher
authors.initials: C
authors.lastname: Saunter
authors.forename: Gordon D
authors.initials: GD
authors.lastname: Love