Colourful imaging and self-reconstruction properties of modified single-focus fractal zone plates.

Abstract

A modified single-focus fractal zone plate (MSFFZP) is proposed to generate a single main focus with many subsidiary foci or two equal-intensity main foci with many subsidiary foci. Widths of high-transmission zones, which have influence on the number of the high-order diffraction foci, such as the second-order focus and the fourth-order focus, can adjust first-order fractal focal intensities, but have no influence on first-order focal positions. Moreover, the MSFFZPs have the first-order foci or the first and second order foci only along the optic axis. It is proved numerically and experimentally that the MSFFZP can generate one or two colourful images with the low chromatic aberrations at the focal planes, and the MSFFZP beam has the self-reconstruction property. In addition, the MSFFZP produces a series of foci at the different focal planes along the optic axis in the simulations and experiments. The method of constructing the MSFFZP is illustrated. The proposed zone plate can be used to produce the multiple clear images, trap particles at the multiple planes simultaneously, and generate the images with the low chromatic aberration.