Focusing optics for hard x-/soft gamma-rays (above 100 keV) are in a development phase. One promising method is represented by the Laue lens technology that has already been validated through on-ground prototypes and balloon tests. Laue lens optics will be an outstanding tool for observing weak sources in a notably short integration time thanks to the excellent sensitivity they can provide. Such performances has been further increased with the employ of cylindrical bent crystals that are capable to dramatically narrow the Laue lens Point Spread Function (PSF). One aspect that is under investigation is the image aberrations for off-axis sources. This fact limits the Field of View (FoV) of a Laue lens to few arcmin. The employ of bent crystals in double diffraction configuration would reduce the mentioned aberration, increasing the FoV of the resulting Laue lens. Double diffraction crystals would represent an extension to hundreds of keV of the Lobster Eye (LE) principles that is well tested for focusing < 10 keV photons. We investigate pros and cons of the double diffraction configuration with respect to the single diffraction through Monte Carlo simulations and we compare their performances in terms of efficiency, PSF, pass-band and effective area. We also present preliminary tests performed at the LARIX facility to evaluate the technical feasibility of crystals with the aforementioned characteristics.
Hard X-ray astronomy is a crucial field for understanding physical processes occurring in several celestial objects, characterized by extreme physical conditions and strong gravity regime, but still poorly explored. Current hard-X ray instrumentation suffers from a poor angular resolution, compared with other wavelengths, and insufficient continuum sensitivity to resolve hard X-ray spectra, especially above few hundreds keV. Laue lenses made with bent crystals represent a viable solution to overcome both limitations, providing good angular resolution ( better than 30 arcsec) combined with excellent sensitivity (orders of magnitude better than that achievable with the current non focusing instrumentation). Supported by the Italian Space Agency, we test a modular method for building Laue lenses. This consists in the realization of portions of Laue lenses that are successively tuned and aligned under the control of a gamma-ray source for focusing the radiation on the common Laue lens focal point. Each module, composed with few tens of crystals, can be realized with an accuracy better than 20 arcsecs with the goal of achieving an overall alignment better than 30 arcsec. In addition, we present a significant improvement in the realization of a large number of bent crystals with the required curvature.
The ATHENA X-ray telescope comprises an optical system with several hundreds of Silicon Pore Optics (SPO) Mirror Modules (MM) to be assembled. All the MMs have to be tested for acceptance before integration. INAF-Osservatorio Astronomico Brera is building in its premises of Merate (Italy) a unique pathfinder facility, BEaTriX, which is characterized by a broad (170 ×60 mm2), uniform and parallel X-ray beam (divergence ≤ 1.5 arcsec HEW) at the energies of 1.49 and 4.51 keV. BEaTriX prime goal is to prove that it is possible to perform the acceptance tests (PSF and Aeff) of the ATHENA SPO MM’s at the production rate of 3 MM/day. The system is very compact (9 × 18 m2) and it is designed with modular compartments where the vacuum can be broken independently to replace the optics under test. It works at a vacuum level of 10-3 mbar, easily evacuated in a short time. The expanded and parallel beam is obtained with an X-ray microfocus source placed in the focus of a paraboloidal mirror, a monochromation stage with 4 symmetrically cut crystals, and an expansion stage where the beam is diffracted and expanded by an asymmetrically-cut crystal. The key axes of all the optical components are motorized in vacuum for a proper beam alignment. The expanded beam fully illuminates the aperture of the MMs, imaging the focused beam at 12 m distance on a CCD camera, with the sensor in vacuum and motorized in air for XYZ movements. A thermal box is also present to radiatively heat the MM and check its optical performances under different temperatures. The design of the facility started in 2012 and has been finalised under an ESA contract. After completing the design, the facility is now in the realization phase. This paper provides an overview of the current status of the facility realization.