A versatile two/four crystal monochromator for X-ray absorption spectroscopy

This paper describes a unique X-ray monochromator which can employ either two or four crystal reflections. In the four crystal mode two counter-rotating pairs of crystals provide a high resolution despersive arrangement with a fixed output beam. In this arrangement the basic functions of the monochromator are separated: The first crystal takes the heat load, the second and third crystals provide energy resolution, and the fourth crystal can be bent for sagittal focusing. The advantages of this design for use with a collimating mirror is discussed along with a comparison of two and four crystal characteristics. Operation in both two and four crystal modes is described along with procedures for maintaining crystal alignment. (orig.)