High-resolution monochromator for soft and hard x rays

An x-ray monochromator for the range from 800 eV to 10 keV has been designed, constructed, and tested at LNLS. The high resolution is achieved by a four-crystal scheme where two nondispersive double crystals (or channel-cut crystals) are arranged in the dispersive configuration. Each double crystal is installed on the axis of a precision-machined cylindrical plate. Synchronized counterrotation of both plates is achieved by a single high precision translation stage connected to them by thin metallic tapes or wires. This mechanical design makes it very stable and easy to implement as a compact ultrahigh-vacuum unit, since only one translation has to be transmitted into the monochromator vessel. To characterize the prototype we used the Cu K lines of a conventional x-ray tube and two Si(422) channel-cut crystals, yielding an angular acceptance of 2.6 arcsec and an energy resolution of 10−5. The stability of the whole system turned out to be better than 0.6 arcsec for several hours. We swept several times the angle from Cu Kα1,2 to Cu Kβ (about 5.6°) and the position was reproduced within the same accuracy of 0.6 arcsec.