A Single Focus Helical Zone Plate

Abstract

The invention discloses a single-focus helical zone plate, which comprises a transparent substrate, an opaque metal layer is arranged on the transparent substrate, and the opaque metal layer is composed of randomly distributed helical elements; the randomly distributed helical The primitives are obtained by the following method: Divide each period of the traditional helical zone plate into N parts, each of which is a helical primitive, and these helical primitives are at the inner and outer diameter r i and r o Randomly distributed along the radial direction, a large number of primitives are randomly distributed along the radial direction to form a single-focus helical zone plate that tends to have a cosine transmittance function, and can produce an optical vortex with only the first-order diffraction focus. The invention overcomes the disadvantage that the general helical zone plate has multi-level focal points, and has only one-order diffraction focus, which can improve the imaging contrast when used for enhanced imaging at the edge of the helical zone plate.

Description

technical field [0001] The invention belongs to the technical field of diffractive optics, in particular to a single-focus helical zone plate. Background technique [0002] People began to pay attention to and study the optical vortex from the 1930s. At that time, Airy discovered that after the beam passed through the lens, there was a strange spiral spot on the focal plane. The central light intensity of the vortex beam is zero on the axis, so it is also called a hollow beam. Moreover, the physical properties of the vortex beam are unique. The light intensity is distributed in a ring during the propagation of the beam, and the wavefront structure is helical. The expression of the light field contains a phase factor: where p is the topological charge of the vortex beam. The size of the dark core in the central region is small, and there is no heating damage effect when manipulating the particles. In addition, the optical vortex also carries orbital angular momentum duri...

AI Technical Summary

Problems solved by technology

However, this method of modulating the transmittance function of the helical zone plate through the window function inevitably reduces the light transmission of the helical zone plate and reduces its diffraction efficiency.

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