Proof-of-concept Talbot–Lau x-ray interferometry with a high-intensity, high-repetition-rate, laser-driven K-alpha source

Abstract

Talbot-Lau x-ray interferometry is a grating-based phase-contrast technique, which enables measurement of refractive index changes in matter with micrometric spatial resolution. The technique has been established using a variety of hard x-ray sources, including synchrotron, free-electron lasers, and x-ray tubes, and could be used in the optical range for low-density plasmas. The tremendous development of table-top high-power lasers makes the use of high-intensity, laser-driven K-alpha sources appealing for Talbot-Lau interferometer applications in both high-energy-density plasma experiments and biological imaging. To this end, we present the first, to the best of our knowledge, feasibility study of Talbot-Lau phase-contrast imaging using a high-repetition-rate laser of moderate energy (100 mJ at a repetition rate of 10 Hz) to irradiate a copper backlighter foil. The results from up to 900 laser pulses were integrated to form interferometric images. A constant fringe contrast of 20% is demonstrated over 100 accumulations, while the signal-to-noise ratio continued to increase with the number of shots. Phase retrieval is demonstrated without prior ex-situ phase stepping. Instead, correlation matrices are used to compensate for the displacement between reference acquisition and the probing of a PMMA target rod. The steps for improved measurements with more energetic laser systems are discussed. The final results are in good agreement with the theoretically predicted outcomes, demonstrating the applicability of this diagnostic to a range of laser facilities for use across several disciplines.

Phase imaging of irradiated foils at the OMEGA EP facility using phase-stepping X-ray Talbot–Lau deflectometry

“…The Talbot effect exhibits itself in the fact that when a coherent wave is diffracted by a periodic grating, an exact replica of the grating is observed at a distance (called the Talbot length) from the grating. On top of that, at fractional distances of this length, a similar image, with different periodicity, is also produced [ 4 , 5 ] . The distances of interest are denoted as , where is an integer number called the Talbot order (even for transmission gratings, and odd for phase gratings).…”

“…However, a series of smaller and locally coherent sources can be generated through the Lau effect by placing an additional diffraction grating between the source and the interferometer. Under the right conditions, this so-called source grating can generate an interference pattern [ 4 ] .…”

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

“…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 ]. Experiments striving the goal of imaging laser-driven 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. At the PHELIX facility, the propagation-based phase-contrast imaging of laser-induced shock waves [ 23 , 24 ] was conducted.…”

“…As a proof of principle measurement at a laboratory X-ray tube with a three-grating setup, they combined a single-shot object image with reference images acquired using phase-stepping. In 2020, Bouffetier et al [ 22 ] managed to average a large amount of images taken with a three-grating Talbot–Lau setup at a high-repetition-rate backlighter K- α source and reconstruct low-noise images from that. If the X-ray source has sufficient spatial coherence, the source grating can be omitted [ 14 , 28 ], allowing us to use a two-grating setup.…”

“…The objective of this work is to compare two methods for improving image quality by using multiple reference images acquired with different X-ray spectra and source positions. The standard method combines multiple references into one average reference image before the reconstruction [ 22 ]. The other method combines the different images after reconstruction.…”