The oblique incidence of a He-Ne laser beam onto a phase-only diffractive optical element (DOE) that simultaneously produces several unimode different-order Bessel beams propagating at various angles with respect to the optical axis is studied theoretically and experimentally. It is shown that, under obliquely incident illumination of a DOE that forms Bessel beams, the resulting astigmatic diffraction pattern can be used to unambiguously identify the direction of the Bessel beam's phase rotation and the order of the Bessel mode.
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