In-line holography with hard x-rays at sub-15 nm resolution

J Soltau,T Salditt,M Vassholz,M Osterhoff

doi:10.1364/optica.420060

Abstract

X-ray in-line holography is well suited for three-dimensional imaging, since it covers a large field of view without the necessity of scanning. However, its resolution does not extend to the range covered by coherent diffractive imaging or ptychography. In this work, we show full-field holographic x-ray imaging based on cone-beam illumination, beyond the resolution limit given by the cone-beam numerical aperture. Image information encoded in far-field diffraction and in holographic self-interference is treated in a common reconstruction scheme, without the usual empty beam correction step of in-line holography. An illumination profile tailored by waveguide optics and exactly known by prior probe retrieval is shown to be sufficient for solving the phase problem. The approach paves the way toward high-resolution and dose-efficient x-ray tomography, well suited for the current upgrades of synchrotron radiation sources to diffraction-limited storage rings.

Highlights

Coherent x-ray optics have led to transformative progress in recent years [1,2,3], opening up novel opportunities to image matter at high resolution [4,5,6], with chemical sensitivity [7], and at ultrafast time scales [8,9]
We extend the classical work [31,32] by a few important modifications, which result in significant improvements of the image quality: (1) We exchange the Fresnel zone plate (FZP) by an x-ray waveguide (WG) optic, generating a compact source spot at the WG exit but a highly curved wavefront at zOb. (2) We reconstruct the probe P by ptychography before the single-frame acquisition of the object O. (3) We use a modified reconstruction scheme that is not based on subtraction of the probe
We show that the usual sampling constraints can be overcome, i.e., the field of view (FOV) at zOb can be larger than the critical value calculated from the detector pixel size px according to the classical oversampling criterion [33]

Summary

Introduction

Coherent x-ray optics have led to transformative progress in recent years [1,2,3], opening up novel opportunities to image matter at high resolution [4,5,6], with chemical sensitivity [7], and at ultrafast time scales [8,9]. For nondestructive imaging of three-dimensional (3D) bulk materials and biological specimens, hard x-ray inline holography or propagation imaging is suitable [10,11,12], since it offers a phase-sensitive imaging scheme that can cover large specimens in a full-field approach without the need for scanning. Contrast formation is based on wave propagation and self-interference of the scattered and primary beam behind the object. In contrast to coherent diffractive imaging (CDI), the phase problem of holographic imaging is mathematically better posed [16] due to the near-field interference between a scattered wave and a reference wave. Based on its full-field nature and its dose efficiency, propagation imaging is well suited for 3D imaging of biological soft tissues [20,21,22,23] as well as for dynamic imaging [24]

Methods

Results

Conclusion