Diamond crystal optics for self-seeding of hard X-rays in X-ray free-electron lasers

Abstract We report design, fabrication, and results of X-ray topography characterization of thin synthetic type IIa diamond crystal plates and crystal-holder assemblies developed for the Hard X-ray Self-Seeding project at the Linac Coherent Light Source. The goal of the project was to achieve generation of fully coherent hard X-rays using the self-seeding concept and the single-crystal diamond wake monochromator [Geloni et al., J. Mod. Opt. 58, 1391 (2011)]. High crystal quality, crystal thickness of ≈ 0.1–0.2 mm and strain-free crystal mount were the main requirements. Nearly defect-free diamond plates of (001) orientation, with thicknesses of 0.1 mm and 0.15 mm, and of a trapezoidal shape were fabricated and preliminarily evaluated. The plates were further characterized using X-ray topography. These tests helped to minimize strain in crystals induced by mounting in crystal holders and to determine defect-free crystal regions. Self-seeding experiments were conducted at the Linac Coherent Light Source using the diamond plates and crystal-holder assemblies selected by our studies. Fully coherent 8.33-keV X-rays with 5 × 10− 5 relative bandwidth were produced [Amann et al., Nat. Photonics 6, 693 (2012)].