A simple, efficient and robust experimental scheme to characterize vortex beams is demonstrated. When a vortex beam, described by a Laguerre-Gauss beam with winding number m
and radial index p
=0, impinges on a diffraction grating having a quadratic curvature on its lines, the output beam in the first diffraction order consists of a set of elongated intensity spots. The number N
of spots determines the absolute value of the integer m
), and the sign of m
is given by the direction of elongation of the spots. The detection scheme is extremely simple, low cost and reliable. It is robust since it is insensitive to the relative locations of the beam axis and the grating center, and it works even when the impinging angle on the grating plane might change. It is efficient since most of the energy of the output beam is in the diffraction order of interest for vortex characterization. It would be interesting to see if the method can also be used to determine the radial number p
when this is different from zero, or to characterize superpositions of vortex beams with different winding numbers.
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