X-RAY OPTICAL CONSIDERATIONS ON PARABOLIC GRADED MULTILAYERS ON THE DIFFRACTED BEAM SIDE IN X-RAY DIFFRACTION

Parabolically curved graded multilayer mirrors, so-called Gobel mirrors, have opened up new applications as x-ray optical devices. They are applied as condensing reflectors to convert divergent x-rays from laboratory x-ray sources into a parallel beam. The use of such graded multilayers on the diffracted beam side of x-ray scattering experiments is an interesting alternative to the state of the art analyzer crystals. As medium resolution analyzers in tripleaxis diffractometry, graded multilayers allow to distinguish between different real structure effects in epitaxial sample systems. For the application on the diffracted beam side in parallel beam optics, the resolution properties of the parabolically curved graded multilayer mirror have to be examined. Therefore, a new method has been developed to prove the focussing properties of adjacent area elements on the mirror. As medium resolution analyzers with high intensity troughput, parabolically curved graded multilayers are ideally suited to cover the range of resoluton limited by soller slits on the low-resolution side and by crystals on the highresolution side. The performance of mirrors applied as analyzers is demonstarted on epitaxial GaN layers and compared with the performance of an analyzer crystal.