Measurement of the fractional orbital angular momentum of asymmetric laser beams by using two cylindrical lenses

Here we propose and study both theoretically and experimentally a simple and high-efficient technique for measuring the orbital angular momentum (OAM) of paraxial laser beams. The technique uses two intensity distributions measured in the foci of two perpendicular cylindrical lenses. For these distributions, first-order intensity moments are calculated, which allow the OAM to be easily obtained. The experimental error increases from ∼1% for small fractional OAM (up to 4) to ∼8% for large fractional OAM (up to 30). We also show numerically that the proposed technique allows to determine the OAM if the beam is distorted by a phase diffuser in the initial plane. (paper)