Bypassing the resolution limit of diffractive zone plate optics via rotational Fourier ptychography

TL;DR

This paper introduces a rotational Fourier ptychography method that surpasses the traditional resolution limits of diffractive zone plate optics by using sample rotations and image processing, enabling higher resolution imaging without fabricating ultra-fine zones.

Contribution

The authors demonstrate a novel approach combining sample rotation and Fourier ptychography to bypass the fabrication resolution limit of zone plates, achieving significant resolution enhancement.

Findings

Achieved 8-fold resolution improvement in experiments.

Resolution is limited by maximum out-of-plane rotation angle, not zone width.

Method enables high-resolution imaging without ultra-fine zone fabrication.

Abstract

Diffractive zone plate optics uses a thin micro-structure pattern to alter the propagation direction of the incoming light wave. It has found important applications in extreme-wavelength imaging where conventional refractive lenses do not exist. The resolution limit of zone plate optics is determined by the smallest width of the outermost zone. In order to improve the achievable resolution, significant efforts have been devoted to the fabrication of very small zone width with ultrahigh placement accuracy. Here, we report the use of a diffractometer setup for bypassing the resolution limit of zone plate optics. In our prototype, we mounted the sample on two rotation stages and used a low-resolution binary zone plate to relay the sample plane to the detector. We then performed both in-plane and out-of-plane sample rotations and captured the corresponding raw images. The captured images were processed using a Fourier ptychographic procedure for resolution improvement. The final achievable resolution of the reported setup is not determined by the smallest width structures of the employed binary zone plate; instead, it is determined by the maximum angle of the out-of-plane rotation. In our experiment, we demonstrated 8-fold resolution improvement using both a resolution target and a titanium dioxide sample. The reported approach may be able to bypass the fabrication challenge of diffractive elements and open up new avenues for microscopy with extreme wavelengths.