Single-distance phase retrieval algorithm for Bragg Magnifier microscope.

Stanislav Hrivňak,Tilo Baumbach,Hartmut Greven,Dušan Korytár,Elias Hamann,Zdenko Zápražný,Christoph Rau,Patrik Vagovič,Ladislav Mikeš,Angelica Cecilia,Ulrich H Wagner,Libor Švéda,Jozef Uličný,Eva Gimenez-Navarro

doi:10.1364/oe.24.027753

Abstract

We present an improved, single-distance phase retrieval algorithm applicable for holographic X-ray imaging of biological objects for an in-line germanium Bragg Magnifier Microscope (BMM). The proposed algorithm takes advantage of a modified shrink-wrap algorithm for phase objects, robust unwrapping algorithm as well as other reasonable constraints applied to the wavefield at the object and the detector plane. The performance of the algorithm is analyzed on phantom objects and the results are shown and discussed. We demonstrated the suitability of the algorithm for the phase retrieval on a more complex biological specimen Tardigrade, where we achieved successful phase retrieval from only a single hologram. The spatial resolution obtained by Fourier spectral power method for biological objects is ∼ 300 nm, the same value as obtained from the reconstructed test pattern. Our results achieved using the new algorithm confirmed the potential of BMM for in-vivo, dose-efficient single-shot imaging of biological objects.

Highlights

Cut crystal used for magnification of an X-ray beam and its application for X-ray imaging was firstly proposed and demonstrated by Kohra [1] for one dimensional magnification
We present an improved, single-distance phase retrieval algorithm applicable for holographic X-ray imaging of biological objects for an in-line germanium Bragg Magnifier Microscope (BMM)
The work is structured in a following way: Section 2 describes the image formation and the design of the algorithm, in Section 3 we show the performance of the algorithm on the measured data and the last section contains the summary of this work and further prospects towards the in-vivo biological X-ray imaging and ultra-fast X-ray imaging

Summary

Introduction

Cut crystal used for magnification of an X-ray beam and its application for X-ray imaging was firstly proposed and demonstrated by Kohra [1] for one dimensional magnification. The problem of limited operational energy has been overcome by a variable magnification system composed of two crossed silicon crystals [9], where one can vary the effective asymmetry angle over the entire range covering maximum magnification to maximum compression for fixed energy. Narrow angular diameters of new X-ray sources, especially X-ray Free Electron Lasers with their spectral bandwidths which are matching or are smaller than the angular-spectral acceptance of BMM, will increase the throughput of this microscope to its maximum limited only by the peak reflectivity of the used crystal. The detection sensitivity is especially important, when the imaging is performed in holographic mode, where the sample is placed far enough in front of BMM and the spatial resolution is determined by the visibility of outermost finest Fresnel oscillations. The work is structured in a following way: Section 2 describes the image formation and the design of the algorithm, in Section 3 we show the performance of the algorithm on the measured data and the last section contains the summary of this work and further prospects towards the in-vivo biological X-ray imaging and ultra-fast X-ray imaging

Theory and algorithm

Results and discussion

Conclusion