Silicon single crystal as back-reflector for high-intensity hard x-rays

At the Lawrence Livermore National Laboratory (LLNL) we have engineered a silicon prototype sample that can be used to reflect focused hard x-ray photons at high intensities in back-scattering geometry. 1 Our work is motivated by the need for an all-x-ray pump-and-probe capability at X-ray Free Electron Lasers (XFELs) such as the Linac Coherent Light Source (LCSL) at SLAC. In the first phase of our project, we exposed silicon single crystal to the LCLS beam, and quantitatively studied the x-ray induced damage as a function of x-ray fluence. The damage we observed is extensive at fluences typical of pump-and-probe experiments. The conclusions drawn from our data allowed us to design and manufacture a silicon mirror that can limit the local damage, and reflect the incident beam before its single crystal structure is destroyed. In the second phase of this project we tested this prototype back-reflector at the LCLS. Preliminary results suggest that the new mirror geometry yields reproducible Bragg reflectivity at high x-ray fluences, promising a path forward for silicon single crystals as x-ray back-reflectors.