High order reflectivity of highly oriented pyrolytic graphite crystals for x-ray energies up to 22 keV.

We used Kr Kα (12.6 keV), Zr Kα (15.7 keV), and Ag Kα (22.2 keV) x-rays, produced by petawatt-class laser pulses, to measure the integrated crystal reflectivity R_int of flat highly oriented pyrolytic graphite (HOPG) up to the fifth order. The maximum R_int was observed in first order (3.7 mrad at 12.6 keV), decreasing by a factor of 3–5 for every successive order, and dropping by a factor of 2–2.5 at 22.2 keV. The current study indicates that HOPG crystals are suitable for measuring scattering signals from high energy x-ray sources (E≥20 keV). These energies are required to penetrate through the high density plasma conditions encountered in inertial confinement fusion capsule implosions on the National Ignition Facility. [ABSTRACT FROM AUTHOR]