A proposal for a 1D-imaging broadband x-ray crystal spectrometer enabled by a sagittally focusing x-ray mirror

Measurements of x-ray absorption/opacity in ionized plasmas at the National Ignition Facility in experiments with high neutron yields require large detector standoff distances, motivating advances in opacity spectrometer design. We propose a spectrometer in which x rays first reflect from a sagittally focusing mirror with a variable-radius sagittal profile. The mirror sets the sagittal imaging condition so that, after subsequent reflection from a meridionally bent crystal, the x rays form a sagittally focused spectrum at the detector plane. The crystal provides spectral dispersion in the meridional direction, while sagittal focusing by the mirror enables 1D imaging of an emitting (or backlit) object. The basic characteristics of the spectrometer are described analytically. The imaging performance of a selected high-magnification design is studied numerically via ray tracing. We show that a large spectral range (Emax - Emin)/E0 ≃ 1/2, high spectral resolving power E/ΔE ≃ 1000, high magnification, M ≃ 10, and 1D spatial resolution of better than 100 μm can be achieved simultaneously.