Thick self-standing bent crystals as optical elements for a Laue lens for applications in astrophysics

In this paper we report progresses in the realization of self-standing bent crystals, which are suitable as optical elements for Laue lenses, i.e. for optic to focus hard X-rays in the 100–1000 keV energy range. The curvature of the crystals is a key factor to enhance diffraction efficiency and energy bandpass for such an optic. In particular, two bent crystals featuring a thickness of 5 mm, made of Si and Ge respectively, were produced at the Sensor and Semiconductor Laboratory in Ferrara, Italy. The crystals were bent through the application of a carbon fibre composite. This proved to be a relatively low cost method for crystal bending, suitable for mass production. The manufactured samples were characterised via optical interferometry, and showed a fairly uniform curvature. Finally, the samples were tested exploiting hard X-ray diffraction at the ID11 facility of the European Synchrotron Radiation Facility (ESRF) in Grenoble, France. A careful analysis of the experimental data highlighted that the samples feature large energy bandpass, wide geometrical acceptance for incoming hard X-rays, and high diffraction efficiency. We therefore conclude that such self-standing crystals are good candidates as Laue lens components for astrophysics applications.