Optimization of dynamically bent crystals for X-ray focusing monochromators

It is well known that one can use a sagittally bent second crystal in order to increase horizontal angular acceptance of a double crystal monochromator. A dynamically bent second crystal in such a monochromator with 6 mrad horizontal acceptance has been studied and the anticlastic distortions were calculated by means of finite element modeling. It was decided that in order to decrease the undesirable bending of the crystal in the meridional direction, stiffening ribs would be cut on its non-working surface. The design of the second monochromator crystal was optimized with respect to the calculated performance and also to the crystal manufacturing process. The optimum design was found to be a crystal with seven stiffening ribs on its non-working surface, which was duly manufactured.