Reducing the focal spot size under radially polarized illumination by means of a binary annular element
S.N. Khonina, A.V. Ustinov

Full text of article: Russian language.

Abstract:
The influence of the width of a ring diaphragm with a radial phase jump on the focal spot size and intensity under the radially polarized illumination is analytically and numerically investigated . It is show n t hat due to the destructive interference of the different-phase rings , it is possible to overcome the scalar limit corresponding to the first zero of the zero-order Bessel function . Thus , the minimal focal spot size (FWHM = 0,33l) is reached at the ring diaphragm width equal to 20% of the full aperture radius . In this cas e, the i ntensity of the side lobes does not exceed 30% of that of the central peak. It is also sh ow n t hat due to introducing the phase jump and simultaneous ly widening the ring aperture it is possible to generate a focal spot whose size does not exceed a limit corresponding to the narrow ring aperture, while the intensity increases almost 6 times. In this case , the side lobes are increasing to 35% of the central peak.

Key words:
sharp focusing, radial polarization, narrow ring aperture, radial phase jump, focal spot reduction , side lobe intensity .

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