Coherent Diffractive Imaging Using Randomly Coded Masks

TL;DR

This paper introduces a novel extension to coherent diffractive imaging (CDI) that uses randomly coded masks to encode additional information, enabling high-resolution X-ray imaging without traditional object constraints, demonstrated with laser experiments.

Contribution

The work presents an experimental demonstration of using multiple randomly coded masks in CDI to improve phase retrieval, reducing reliance on object-domain constraints and enhancing imaging stability.

Findings

Reliable phase convergence with 3-4 masks

Enhanced image reconstruction quality

Potential for rapid prototyping in X-ray imaging

Abstract

Coherent diffractive imaging (CDI) provides new opportunities for high resolution X-ray imaging with simultaneous amplitude and phase contrast. Extensions to CDI broaden the scope of the technique for use in a wide variety of experimental geometries and physical systems. Here, we experimentally demonstrate a new extension to CDI that encodes additional information through the use of a series of randomly coded masks. The information gained from the few additional diffraction measurements removes the need for typical object-domain constraints; the algorithm uses prior information about the masks instead. The experiment is performed using a laser diode at 532.2 nm, enabling rapid prototyping for future X-ray synchrotron and even free electron laser experiments. Diffraction patterns are collected with up to 15 different masks placed between a CCD detector and a single sample. Phase retrieval is performed using a convex relaxation routine known as "PhaseCut" followed by a variation on Fienup's input-output algorithm. The reconstruction quality is judged via calculation of phase retrieval transfer functions as well as by an object-space comparison between reconstructions and a lens-based image of the sample. The results of this analysis indicate that with enough masks (in this case 3 or 4) the diffraction phases converge reliably, implying stability and uniqueness of the retrieved solution.