Novel Methods for Hard X-ray Holographic Lensless Imaging

Holography is a coherent imaging method that provides complex-valued reconstructions of the wave field at the exit of a sample by virtue of the interference between the scattered sample wave and a reference wave [1]. Fourier transform holography (FTH) is a robust and reliable method where reconstructions are obtained by a single Fourier transform, owing to a nearby point-scatterer whose transmission function is approximated to a delta function [2]. Hence, the total autocorrelation function includes the cross-correlation between the sample function and the delta-like reference function, leading to two separated twin images of the sample. Holographic techniques emerged using different types of reference structures such as extended references [3] (slits, corner apertures, etc.), uniformly redundant arrays, and customised references [4]. Such methods have been successfully implemented using soft Xrays [2,3,4,5]. However, for hard X-rays, the fabrication of high-resolution fully absorbing reference masks is almost impossible. Therefore, high-resolution holographic diffraction imaging with hard Xrays requires a solution to the fabrication limitations. Furthermore, for an absorbing mask, most methods have also employed a “monolithic” frame [5] where the reference and sample are bound on the same substrate. This limits the flexibility of the setup and inhibits independent translation and rotation.