A double‐crystal (n,−n) x‐ray monochromator with sagittally bent second crystal for arbitrarily divergent radiation

The maximum transmitted intensity through a (n,−n) double‐crystal x‐ray monochromator with sagittally (cylindrically) bent second crystal takes place when the virtual source lies on the surface of the cylinder. In this case all beams diffracted from the first flat crystal are also diffracted from the second cylindrically bent crystal. The magnification in this case is exactly 1/3 independently of Bragg angle.