Laser-wakefield accelerators for high-resolution X-ray imaging of complex microstructures

Laser-wakefield accelerators (LWFAs) are high acceleration-gradient plasma-based particle accelerators capable of producing ultra-relativistic electron beams. Within the strong focusing fields of the wakefield, accelerated electrons undergo betatron oscillations, emitting a bright pulse of X-rays with a micrometer-scale source size that may be used for imaging applications. Non-destructive X-ray phase contrast imaging and tomography of heterogeneous materials can provide insight into their processing, structure, and performance. To demonstrate the imaging capability of X-rays from an LWFA, we have examined an irregular eutectic in the aluminum-silicon (Al-Si) system. The lamellar spacing of the Al-Si eutectic microstructure is on the order of a few micrometers, thus requiring high spatial resolution. We present comparisons between the sharpness and spatial resolution in phase contrast images of this eutectic alloy obtained via X-ray phase contrast imaging at the Swiss Light Source (SLS) synchrotron and X-ray projection microscopy via an LWFA source. An upper bound on the resolving power of 2.7 ± 0.3 µm of the LWFA source in this experiment was measured. These results indicate that betatron X-rays from LWFA can provide an alternative to conventional synchrotron sources for high resolution imaging of eutectics and, more broadly, complex microstructures

Alloy-Free Band Gap Tuning across the Visible Spectrum

We present evidence, from theory and experiment, that ZnSnN2 and MgSnN2 can be used to match the band gap of InGaN without alloying—by exploiting cation disorder in a controlled fashion. We base this on the determination of S, the long-range order parameter of the cation sublattice, for a series of epitaxial thin films of ZnSnN2 and MgSnN2 using three different techniques: x-ray diffraction, Raman spectroscopy, and in situ electron diffraction. We observe a linear relationship between S2 and the optical band gap of both ZnSnN2 (1.12–1.98 eV) and MgSnN2 (1.87–3.43 eV). The results clearly demonstrate the correlation betweencontrolledheterovalentcationorderingandtheopticalbandgap,whichappliestoabroadgroupof emerging ternary heterovalent compounds and has implications for similar trends in other material properties besides the band gap

Author Correction: Laser-wakefield accelerators for high-resolution X-ray imaging of complex microstructures

An amendment to this paper has been published and can be accessed via a link at the top of the paper