Focusing x-rays to a 1 μm spot using elastically bent, graded multilayer-coated mirrors

Abstract

In the LBNL x-ray fluorescence microprobe, a synchrotron source of x-rays is demagnified several hundred times using a pair of mirrors in the Kirkpatrick-Baez configuration. These are coated with multilayers to increase reflectivity and limit the pass band of the x-rays striking the sample. With spherical mirrors, the spot size obtained is limited by spherical aberration. This can be corrected by using an initially flat mirror elastically bent by a combination of end couples into an ellipse. By grading the multilayer coatings in d-spacing, the throughput of the focusing system is increased and the pass band narrowed. A pair of such mirrors, installed in the microprobe on a bending magnet at the Advanced Light Source (ALS), achieved focal spots of dimensions 1μm×1 μm at energies of 8.5 keV and 12 keV, with an energy pass band of 10%.