  A double-crystal diamond (111) monochromator recently implemented at the
Linac Coherent Light Source (LCLS) enables splitting of the primary X-ray beam
into a pink (transmitted) and a monochromatic (reflected) branch. The first
monochromator crystal with a thickness of 100 um provides sufficient X-ray
transmittance to enable simultaneous operation of two beamlines. Here we report
on the design, fabrication, and X-ray characterization of the first and second
(300-um-thick) crystals utilized in the monochromator and the optical
assemblies holding these crystals. Each crystal plate has a region of about 5 X
2 mm2 with low defect concentration, sufficient for use in X-ray optics at the
LCLS. The optical assemblies holding the crystals were designed to provide
mounting on a rigid substrate and to minimize mounting-induced crystal strain.
The induced strain was evaluated using double-crystal X-ray topography and was
found to be small over the 5 X 2 mm2 working regions of the crystals.
