Ultrahigh-aspect-ratio beam generation with super-resolution spot

Abstract

Focusing to a small spot along a large depth of focus (DOF) beyond the limits imposed by diffraction has attracted extensive theoretical as well as practical interest. The aspect ratio, defined as the DOF divided by the diameter of spot, has been extended by several schemes with reasonable success, but there is no report that enables one to modulate the aspect ratio as long as possible with sidelobe suppression. In this Letter, we propose a method to generate ultrahigh-aspect-ratio beams (UARBs) by introducing an analytic procedure using Zernike polynomials in the modified iterative Fourier-transform algorithm, and a super-resolution spot is also realized to further extend the aspect ratio. We design the diffractive optical elements that generate UARBs with sidelobe suppression and further experimentally demonstrate a stretched 1602:1 aspect ratio of UARBs with a lateral super-resolution spot, suggesting potential applications for further super-resolution imaging or precision fabrication.