High-reflectivity high-resolution X-ray crystal optics with diamonds

Abstract

Owing to the depth to which hard X-rays penetrate into most materials, it is commonly accepted that the only way to realize hard-X-ray mirrors with near 100% reflectance is under conditions of total external reflection at grazing incidence to a surface. At angles away from grazing incidence, substantial reflectance of hard X-rays occurs only as a result of constructive interference of the waves scattered from periodically ordered atomic planes in crystals (Bragg diffraction). Theory predicts that even at normal incidence the reflection of X-rays from diamond under the Bragg condition should approach 100%-substantially higher than from any other crystal. Here we demonstrate that commercially produced synthetic diamond crystals do indeed show an unprecedented reflecting power at normal incidence and millielectronvolt-narrow reflection bandwidths for hard X-rays. Bragg diffraction measurements of reflectivity and the energy bandwidth show remarkable agreement with theory. Such properties are valuable to the development of hard-X-ray optics, and could greatly assist the realization of fully coherent X-ray sources, such as X-ray free-electron laser oscillators [1][2][3] . Diamond is a material with superlative physical qualities: high mechanical hardness, high thermal conductivity, high dispersion index, high radiation hardness, high hole and electron mobilities, low thermal expansion and chemically inert 4 . Technological applications of diamond crystals are increasing not only in the traditional fields of cutting, grinding and polishing tools, but also in high-tech applications, such as diamond-based electronic devices, wide-bandgap radiation detectors, ultraviolet-emitting diodes, biochemical sensors, high-pressure cells and thermal sinks, to name only a few. Very recently, diamond crystals have been identified as indispensable for the realization of X-ray free-electron laser oscillators (XFELOs), next-generation hard-X-ray sources of the highest average and peak brightness and extremely narrow bandwidth 1,2 . The special role of diamonds in the feasibility of the XFELOs is due to their outstanding reflectivity for hard X-rays in Bragg diffraction, thus far only predicted in theory (Fig. 1a).The high reflectivity of crystals in Bragg diffraction is intimately connected with the perfect crystal structure. Progress in fabrication, characterization and X-ray optics applications of synthetic diamonds was substantial in the past decade [5][6][7][8][9][10][11][12][13] . Still the diamond crystals available commercially as a rule suffer from defects: dislocations, stacking faults, inclusions, impurities and so on. Synthetic high-purity (type IIa, low nitrogen content) crystals grown with a high-pressure, high-temperature technique are generally considered to have the highest crystal quality and the lowest density of defects among commercially available diamonds 10,13 . X-ray topography studies have demonstrated crystals with relatively large 4×4 mm 2 defect-free areas 13 . However, critical outstanding questions remain o...

Three-beam setup for coherently controlling nuclear-state population

“…[12] by investigating also the cases of nuclear coherent population transfer in 113 Cd, 152 Pm, 172 Yb and 223 Ra. The separation of the pump and Stokes beams out of the original XFEL beam requires dedicated x-ray optics such as the diamond mirrors [36][37][38] developed for the XFELO. X-ray reflections can also help tune the intensity of the two beams.…”

Performance of the x-ray free-electron laser oscillator with crystal cavity

“…The properties of diamond, including high peak reflectivity, low absorption, high thermal conductivity, and small coefficients of thermal expansion, make it an ideal material for high-power x-ray Bragg mirrors. Although large-scale, perfect diamond crystals have yet to be produced, the FEL oscillator only requires a small $100 m 2 region to be defect free, which seems to be a realistic possibility [22]. Nevertheless, we also consider alternatives in Table I, including silicon and sapphire mirrors.…”

Performance of a beam-multiplexing diamond crystal monochromator at the Linac Coherent Light Source

“…Recent improvements in High Pressure High-Temperature (HPHT) synthesis processes have shown promising results in improved crystal quality. [24][25][26][27][28][29] A set of diamond crystals of the (111) orientation, mounted on an all-diamond mounting frame assembly, was prepared by the Technological Institute for Superhard and Novel Carbon Materials (TISNCM, Troisk, Russia). They were characterized and optimized at the Advanced Photon Source (APS, Argonne, IL) by high resolution topography and then installed in the XPP LODCM for splitting the FEL beam.…”