Broadband High-Resolution Stigmatic Spectral Imaging in the XUV Range

We describe the experimental implementation of high-resolution soft X-ray spectrographs, which are stigmatic throughout their operating range. The optical configuration comprises a grazing-incidence plane VLS grating and a broadband normal-incidence focusing mirror with an aperiodic multilayer coating structure. The operating range is defined by the aperiodic multilayer mirror in use (Mo/Si: 12.5 – 25 nm; Mo/Be: 11 – 14 nm). The spectral resolution is determined by CCD detector resolution and is numerically equal to the product of the plate scale and the double pixel size. Vertically spaceresolved laser-produced plasma spectra of multiply charged ions are presented. The spatial resolution is equal to about 26 μm, the double pixel size. We discuss the prospect of extending high-resolution stigmatic spectral imaging below 11 nm and outline the data of numerical calculations of broadband normal-incidence mirrors based on aperiodic Ru/Sr and La/B₄C multilayer structures.