Characterization of the focusing performance of axial line-focused spiral zone plates

Axial line-focused spiral zone plates were developed for operation at optical wavelengths. The design, fabrication, and diffraction properties of the proposed element are presented. Numerical results showed that hollow beams could be generated, and that the element can be employed for a multi-wavelength operation. The hollow beam within the focal depth was demonstrated experimentally, using a charge-coupled device camera and sliding guide. The results were consistent with those obtained by the simulations. The proposed optical device exhibits significant potential for various applications including optical manipulation and lithography.