Monochromatic x-ray backlighting is an essential and basic diagnostic in the research area, such as laser or z-pinch driven inertial confinement fusion, high energy density physics and laboratory astrophysics. A monochromatic hard X-ray backlighting system based on transmission logarithmic spiral crystals has been imposed, where the crystal is employed as a monochromator as well as an optical path deflector by taking advantage of the defining characteristic that all X-ray radiated from the pole of the spiral meet the crystal surface at the same angle. According to the model of Laue logarithmic spiral crystal imaging system and ray tracing method, the imaging principle and characteristics are analyzed theoretically, particularly the distance that the monochromatic beam split from the transmitted beam. We have designed and fabricated a logarithmic spiral quartz 2023 (2d=0.2749nm) crystal. Accordingly, the X-ray imaging system has been setup at 17.479 KeV (Mo Kα line), where the monochromatic image and the polychromatic image can be obtained at the same time. The test data and experimental results are presented and discussed. Compared with the most broadly applied monochromatic x-ray backlighting based on the spherically bent crystal, new developed imaging system can achieve higher photo energy and broader field of view.
The laser-induced plasma sources give instantaneous 4π divergent x-ray beams. The x-ray source size and pulse duration depend on the properties of the high-energy laser. Copper is the typical target material giving characteristic photon energies around 8.4keV. Different shapes of bent crystals are widely used as imaging and monochromatizing optics. Focusing and collimating are normally functioned by polycapillary x-ray lenses. Especially, the laterally-graded multilayers are applied as x-ray mirrors, which can reflect hard x-rays with big grazing angles, moderate energy resolution and high reflectivities. To get larger acceptance angel, a higher gradient of bilayer thicknesses from 2nm to 3.6nm within 80mm length scale is designed. And the alignment precision of 10μm is required to make it good performance. The reflected monochromatic x-rays can enhance the traverse coherence for the phase contrast imaging. And multi-frames of the same object can be obtained instantaneously by multi-reflections of the mirrors. The laterally-graded multilayer x-ray mirrors are also used for the pinhole imaging of a Z-pinch target, which benefits from the flat reflection surface and monochromatic imaging.