Abstract
Phase-contrast imaging using X-ray sources with high spatial coherence is an emerging tool in biology and material science. Much of this research is being done using large synchrotron facilities or relatively low-flux microfocus X-ray tubes. An alternative high-flux, ultra-short and high-spatial-coherence table-top X-ray source based on betatron motions of electrons in laser wakefield accelerators has the promise to produce high quality images. In previous phase-contrast imaging studies with betatron sources, single-exposure images with a spatial resolution of 6–70 μm were reported by using large-scale laser systems (60–200 TW). Furthermore, images obtained with multiple exposures tended to have a reduced contrast and resolution due to the shot-to-shot fluctuations. In this article, we demonstrate that a highly stable multiple-exposure betatron source, with an effective average source size of 5 μm, photon number and pointing jitters of <5% and spectral fluctuation of <10%, can be obtained by utilizing ionization injection in pure nitrogen plasma using a 30–40 TW laser. Using this source, high quality phase-contrast images of biological specimens with a 5-μm resolution are obtained for the first time. This work shows a way for the application of high resolution phase-contrast imaging with stable betatron sources using modest power, high repetition-rate lasers.
Highlights
Since the discovery of X-rays by Röntgen in 1896, X-ray based imaging technologies have been indispensible in modern medical, biological and material research
It is reported that when images were obtained with multiple exposures the spatial resolution and the contrast degraded greatly due to the large shot-to-shot fluctuations of the source parameters in self-injection LWFA23
Due to the much smaller position fluctuation of the X-ray source in ionization injection compared with self-injection, multiple-exposure phase-contrast images of biological specimens with 5-μm resolution have been obtained for the first time
Summary
Since the discovery of X-rays by Röntgen in 1896, X-ray based imaging technologies have been indispensible in modern medical, biological and material research. In a LWFA, an ultra-short intense laser pulse propagating in a low density plasma creates a strong wake by pushing the plasma electrons away from its path, forming an ion cavity-like structure[17] This wake carries extremely strong accelerating and focusing fields that can approach 100 GV/m level, which is nearly three orders of magnitude larger than those of conventional accelerators. Preliminary phase-contrast imaging experiments using betatron radiation from self-injection LWFA have been carried out on insect[23,24,25] and mouse[26] samples In these experiments, modest single-exposure image resolutions of 6–70 μm were obtained by using relatively large lasers (60–200 TW). Due to the much smaller position fluctuation of the X-ray source in ionization injection compared with self-injection, multiple-exposure phase-contrast images of biological specimens with 5-μm resolution have been obtained for the first time
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