Chromatic aberration of an asymmetrically cut curved crystal due to the dynamical diffraction effect

Abstract

For the case of an asymmetrically cut curved crystal, x rays having different wavelengths with the same incident angle are reflected toward slightly different directions because of the dynamical diffraction effect. This causes a broadening of the focal spot size even for a point source when an asymmetrically cut crystal is used to obtain demagnified images of the synchrotron radiation sources. This broadening is estimated to be 0.7 mm even for a point source with the optics being currently used on the small angle scattering beam line BL-15A at the Photon Factory. It is important to take this effect into account in the designing of a demagnifying optics using an asymmetrically cut curved crystal.