High-resolution x-ray monochromatic imaging for laser plasma diagnostics based on toroidal crystal

Monochromatic x-ray imaging is an essential method for plasma diagnostics related to density information. Large-field high-resolution monochromatic imaging of a He-like iron (Fe XXV) K_α characteristic line (6.701 keV) for laser plasma diagnostics was achieved using a developed toroidal crystal x-ray imager. A high-index crystal orientation Ge ⟨531⟩ wafer with a Bragg angle of 75.37° and the toroidal substrate were selected to obtain sufficient diffraction efficiency and compensate for astigmatism under oblique incidence. A precise offline assembly method of the toroidal crystal imager based on energy substitution was proposed, and a spatial resolution of 3–7 μm was obtained by toroidal crystal imaging of a 600 line-pairs/inch Au grid within an object field of view larger than 1.0 mm. The toroidal crystal x-ray imager has been successfully tested via side-on backlight imaging experiments of the sinusoidal modulation target and a 1000 line-pairs/inch Au grid with a linewidth of 5 μm using an online alignment method based on dual positioning balls to indicate the target and backlighter. This paper describes the optical design, adjustment method, and experimental results of a toroidal crystal system in a laboratory and laser facility.