Expressions and numerical results are given for diffraction from a circular annular aperture with a helical phase factor in the Fraunhofer approximation. The numerical results for the amplitude function are given for two values of the ratio of the aperture’s inner diameter to outer diameter, namely, 0.8 and 0.9, and for five values of the helical phase factor.
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W. J. Condell (1985) studied this question.
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