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X-ray diffraction efficiency of bent GaAs mosaic crystals for the Laue project

机译：Laue项目的弯曲GaAs镶嵌晶体的X射线衍射效率

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摘要

In a Laue lens made of single crystals oriented to diffract parallel x-rays at the lens focus, the energy and angular resolution are limited by the crystal size and by the crystal mosaicity. The use of extended crystals bent according to the lens curvature provides better focusing, with the resolution given essentially by the crystal mosaicity. With this approach, a crystal mosaicity as low as 15-25 arcsec, well below the mosaicity value of copper crystals, was found suitable for the new design of the Laue lens. The reflectivity and transmission profiles and the integrated intensity have been measured in flat and bent GaAs and Si crystals prepared by the method of surface damaging by using sandpaper of different grain size. The surface grinding induces a local lattice strain which produces a self-standing bent crystal. Bent crystals with radius of curvature lower than a critical value given by the extinction length behave as ideal mosaic crystals, maximizing the diffraction efficiency at high x-ray energies. It is found that the surface grinding does not affect the crystal diffraction efficiency, the damage thickness being limited to a few tens microns near the crystal surface.
机译：在由定向在透镜焦点处衍射平​​行X射线的单晶体制成的劳厄透镜中，能量和角分辨率受晶体尺寸和晶体镶嵌性的限制。根据透镜曲率弯曲的延伸晶体的使用可提供更好的聚焦，而分辨率基本上由晶体镶嵌性决定。通过这种方法，发现低至15-25 arcsec的晶体镶嵌度远低于铜晶体的镶嵌度值，适合于Laue镜片的新设计。在通过使用不同粒度的砂纸通过表面破坏方法制备的平坦且弯曲的GaAs和Si晶体中，测量了反射率和透射曲线以及积分强度。表面研磨会引起局部晶格应变，从而产生自立的弯曲晶体。曲率半径低于消光长度给定的临界值的弯曲晶体表现为理想的镶嵌晶体，从而在高X射线能量下最大化了衍射效率。已经发现，表面研磨不影响晶体的衍射效率，将损伤厚度限制在晶体表面附近的几十微米。

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