title: Quantitative characterization of the energy circulation in helical beams by means of near-field diffraction.
abstract: We present a method to measure the skew angle of the wave-fronts in an optical vortex, which is directly related with the energy flux. It is based on the analysis of the evolution on propagation of the near-field diffraction pattern generated by a single-slit, consisting of two main lobes that shift in opposite directions depending on the vortex helicity. The transverse displacement of each lobe as a function of the propagation distance allows to quantify the energy circulation. Analytical, numerical and experimental results are compared, showing good agreement. We illustrate the method for the case of Bessel beams, although we also discuss other types of helical beams, such as Laguerre-Gauss and Mathieu beams.
authors.affiliation: Instituto de Física, Universidad Nacional Autónoma de México, Apdo. Postal 20-364, 01000 México Distrito Federal, México.
authors.forename: Roland A
authors.initials: RA
authors.lastname: Terborg
authors.forename: Karen
authors.initials: K
authors.lastname: Volke-Sepúlveda
mesh_terms: D000465:Algorithms; D004735:Energy Transfer; D008027:Light; D012031:Refractometry / Q000379:methods*; D012542:Scattering, Radiation