Methods for determining the orbital angular momentum  of a laser beam
    Kotlyar V.V., Kovalev  A.A., Porfirev A.P.
   
  IPSI RAS - Branch of the  FSRC “Crystallography and Photonics” RAS, 
443001, Samara, Russia, Molodogvardeyskaya 151
 Samara National Research University, 443086, Russia, Samara,  Moskovskoye Shosse 34
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Abstract:
We propose and study  numerically and experimentally two methods for determining the orbital angular  momentum (OAM) of paraxial laser beams. One method is based on registering the  intensity in the Fresnel zone, numerically averaging this intensity over the  polar angle at discrete radii, and solving a system of linear equations to find  squared modules of the coefficients of the light field expansion in terms of  basis functions. The other method is based on registering two intensity  distributions in the Fourier plane of two cylindrical lenses rotated 90 degrees  relative to each other, and calculating the first-order moments of the measured  intensities. The experimental error of the OAM determination is about 1% for  small fractional OAM (up to 4), and about 8% for large fractional OAM (up to  30). 
Keywords:
paraxial laser beam,  fractional orbital angular momentum, fractional topological charge, optical  vortex, cylindrical lens, superposition of spatial modes.
Citation:
Kotlyar VV, Kovalev AA,  Porfirev AP. Methods for determining the orbital angular momentum of a laser  beam. Computer Optics 2019; 43(1): 42-53. DOI:  10.18287/2412-6179-2019-43-1-42-53.
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