Distinguishing orbital angular momenta and topological charge in optical   vortex beams
  In this work we discuss how the classical orbital angular momentum (OAM) and topological charge (TC) of optical beams with arbitrary spatial phase profiles are related to the local winding density. An analysis for optical vortices (OV) with non-cylindrical symmetry is presented and it is experimentally shown for the first time that OAM and TC may have different values. The new approach also provides a systematic way to determine the uncertainties in measurements of TC and OAM of arbitrary OV. 
Anderson M. Amaral, Edilson L. Falc\~ao-Filho, Cid B. de Ara\'ujo
physics.optics