A perfect crystal X-ray analyser with meV energy resolution

We present a new method to construct a spherical crystal X-ray energy analyser. The energy analysis is based on high order Bragg reflections from a silicon perfect crystal at angles very close to 90 degrees. In order to preserve the perfect crystal properties in a focusing optics, necessary for meV energy resolution and large angular acceptance, we developed a procedure to mount approximate to 12000 small crystals, obtained from the same silicon wafer, on a spherical substrate. The method is based on computer controlled glueing and cycles of etching for each crystal. We obtained analysers with an energy resolution of 1.7+/-0.5 meV for 21.75 keV X-rays, using the Si(11 11 11) reflection, and with 25 mrad(2) angular acceptance. These analysers have been specifically developed for high energy resolution inelastic X-ray scattering.