ZERO AXIAL IRRADIANCE BY ANNULAR SCREENS WITH ANGULAR VARIATION

For optical alignment, it may be convenient to use a three-dimensional diffraction pattern with zero irradiance along the optical axis. This pattern is created here by using annular screens in the form of a phase daisy, a daisy flower, or a pie, with an even number of slices of an equal central angle and with every other slice with a phase retardation of 180-degrees. We recognize this form of angular variation as a particular solution of a wider set of functions that are able to produce zero axial irradiance.