Focusing properties of mosaic crystals

M. Sanchez del Rio a), M. Gambaccini b), G. Pareschi c), A. Taibi b), A. Tuffanelli b), and A. Freund a)

a)
European Synchrotron Radiation Facility
BP 220, 38043 Grenoble-Cedex, France
b)
Dipartimento di Fisica, Universita di Ferrara and INFN sezione di Ferrara
Via Paradiso 12, I-44100 Ferrara, Italy
c)
Danish Space Research Institute
Juliane Mariies Vej 30, 2100 Copenhagen, Denmark

ABSTRACT

X-ray instruments with mosaic crystals are proposed and used in many applications in synchrotron radiation, medical
physics and astrophysics. These crystals present a parafocusing of the x-ray beam in the diffraction plane, which is
thoroughly analyzed in this paper. We studied the evolution of the cross section of the diffracted beam, using several
samples of Highly Oriented Pyrolythic Graphite crystals coming from different suppliers. The experiment has been
performed at the European Synchrotron Radiation Facility (beamline BM5). The results clearly show a parafocusing
effect in the 1:1 magnification ratio along the diffraction plane and a defocusing effect along the perpendicular plane.
The secondary extinction coeffcient is also measured.

Keywords: Mosaic crystals, Highly Oriented Pyrolytic Graphite (HOPG), x-ray focusing, secondary extinction