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.

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Enrico Virgilli, Giovanni Pareschi, Lisa Ferro, René Hudec, Claudio Ferrari, Sara Beretta, and Vladimir Tichy, "Double diffraction crystals for x-/gamma-ray optics (Conference Presentation)," Proc. SPIE 11119, Optics for EUV, X-Ray, and Gamma-Ray Astronomy IX, 111191D (Presented at SPIE Optical Engineering + Applications: August 15, 2019; Published: 9 September 2019); https://doi.org/10.1117/12.2529363.6084160428001.