Sagittal focusing of high-energy synchrotron X-rays with asymmetric Laue crystals. I. Theoretical considertions

The ability of asymmetric Laue crystals to focus X-rays sagittally is demon strated. The extent of such focusing is similar to that of sagittal focusin g by a Bragg crystal, except for a factor related to the asymmetry angle. T he anticlastic bending facilitates the use of inverse-Cauchois geometry in the meridional plane to provide better energy resolution and to increase th e photon flux by an order of magnitude compared with traditional sagittal f ocusing with Bragg crystals. Furthermore, for sagittal focusing at X-ray en ergies above 30 keV, a Laue crystal is preferred to a Bragg crystal because the length of the beam's footprint on a Laue crystal, unlike on a Bragg cr ystal, is a small and insensitive to energy. The conditions imposed on the asymmetry angle of the Laue crystal to achieve simultaneous sagittal focusi ng and inverse-Cauchois geometry in the meridional plane are derived for bo th single-crystal and double-crystal fixed-exit sagittally focusing monochr omators.