Stack of curved crystals as optical component for hard x- and gamma-ray focusing through a Laue lens

Abstract

A stacking of plate-like curved crystals is proposed as an optical element for realization of a highly efficient Laue lens in astrophysics. Si mono-crystal plates have been bent by surface grooving and positioned one over the other to form a stack. Reciprocal alignment of the curved diffracting planes in the stack has been investigated by hard x-ray diffractometry using a polychromatic and divergent beam. The stack exhibited a single and well-defined focal spot under x-ray diffraction, highlighting that the plates are sufficiently aligned to behave as they were a single crystal. The curvature of the plates in the stack is self-standing and can be highly controlled by adjusting the experimental parameters of grooving. Thanks to the stacking, it would be possible to realize optical elements with arbitrarily large size. This achievement opens up important implications toward the realization of satellite-borne experiments in astrophysics or instruments for nuclear medicine with superior resolution. Surface grooving is easy, cheap, highly reproducible and has been established for Si and Ge, highlighting very high diffraction efficiency over a broad range of energies up to 700 keV, peaking 95% at 150 keV for Si.