Noise Reduction for Single-Shot Grating-Based Phase-Contrast Imaging at an X-ray Backlighter.

Stephan Schreiner,Thilo Michel,Lisa Dietrich,Bernhard Zielbauer,Andreas Wolf,Pascal Meyer,Paul Neumayer,Stefan Funk,Gisela Anton,Veronika Ludwig,Bernhard Akstaller,Max Schuster

doi:10.3390/jimaging7090178

Abstract

X-ray backlighters allow the capture of sharp images of fast dynamic processes due to extremely short exposure times. Moiré imaging enables simultaneously measuring the absorption and differential phase-contrast (DPC) of these processes. Acquiring images with one single shot limits the X-ray photon flux, which can result in noisy images. Increasing the photon statistics by repeating the experiment to gain the same image is not possible if the investigated processes are dynamic and chaotic. Furthermore, to reconstruct the DPC and transmission image, an additional measurement captured in absence of the object is required. For these reference measurements, shot-to-shot fluctuations in X-ray spectra and a source position complicate the averaging of several reference images for noise reduction. Here, two approaches of processing multiple reference images in combination with one single object image are evaluated regarding the image quality. We found that with only five reference images, the contrast-to-noise ratio can be improved by approximately 13% in the DPC image. This promises improvements for short-exposure single-shot acquisitions of rapid processes, such as laser-produced plasma shock-waves in high-energy density experiments at backlighter X-ray sources such as the PHELIX high-power laser facility.

Highlights

Erlangen Centre for Astroparticle Physics (ECAP), Friedrich-Alexander Universität Erlangen-Nürnberg, Karlsruhe Institute of Technology, Institute of Microstructure Technology, Hermann-von-Helmholtz-Platz 1, GSI Helmholtzzentrum für Schwerionenforschung GmbH, Planckstraße 1, 64291 Darmstadt, Germany; Abstract: X-ray backlighters allow the capture of sharp images of fast dynamic processes due to extremely short exposure times
The standard deviation, contrast and contrast-to-noise ratio were initially investigated for the positive differential phase-contrast (DPC) signal
As the used object provides a negative DPC signal, the findings were verified by calculating the contrast-to-noise ratio (CNR) of the corresponding regions of interest (ROI)

Summary

Introduction

This promises improvements for short-exposure single-shot acquisitions of rapid processes, such as laser-produced plasma shock-waves in high-energy density experiments at backlighter X-ray sources such as the PHELIX high-power laser facility. These techniques have been used in the field of laboratory astrophysics with the long-term aim of imaging processes on extremely short time scales Such a process is, e.g., a laser-driven plasma shock wave in a high-energy density experiment. Using a laser-driven X-ray backlighter source for probing these objects enables one to acquire sharp images of these ultra-fast processes If for such an object the X-ray absorption is low, imaging could benefit from the single-shot phase-contrast technique, since it is able to enhance contrast by probing the phase-shifting properties of a plasma [19,20]. Plasma shock waves with phase-contrast were performed on high-power laser facilities such as Omega EP [21] and CELIA [22] with a Talbot–Lau setup consisting of three gratings

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Conclusion