Journal Article diamond X-ray optics free-electron lasers Bragg diffraction Bragg reflectivity Research Support, Non-U.S. Gov't SASE XFEL spectrometers X-ray Bragg diffraction X-ray free-electron laser oscillators X-ray free-electron lasers X-rays XFELs beam conditioning bent diamond crystals crystals diamond monochromators dynamical diffraction electron-energy jitter hard X-rays in-line spectrometers laser ablation radiation damage refractive lenses self-amplified spontaneous emission self-seeding silicon slope errors strongly bent thin diamond crystals