<title>Stigmatic broadband spectroscopic instruments below 300 A</title>

Abstract

Along with ultrahigh-resolution narrow-band spectrometers, a demand exists for medium- and high-resolution stigmatic instruments of a survey type, covering a spectral range of more than a hundred angstroms. Here, we describe several stigmatic spectroscopic configurations intended for characterizing various soft x-ray radiation sources (laser- produced plasmas, XUV lasers, etc.) and optical components [multilayer mirrors (MMs), absorption filters, etc.] in a broad spectral range. The combination of a grazing-incidence toroidal mirror and a large-area transmission diffraction grating (TG) made up a broadband spectrograph with a medium dispersion, with a plate scale of 4-to-20 angstrom/mm, which has proven to be inherently suited for characterizing plane MMs and the laser-plasma source itself. Two versions of W- coated toroidal mirrors were used, which operated at grazing angles of 7.6 degrees and 4 degrees and had respective practical short-wave cutoffs at about 40 and 15 angstrom. Line spectra of low-Z targets and quasicontinuous spectra of a tungsten target were obtained with a resolution of about 800. The configuration of a TG spectrograph was used to characterize CoC MMs with a d-spacing of 38 angstroms fabricated on Si(111) substrates by e-beam deposition and Kr<SUP>+</SUP> ion beam polishing of metal layers. The absolute reflectivities near 75 angstrom were measured at 10%. The combination of a large-area TG and a concave MM with a strong lateral gradient of the d-spacing made up a stigmatic spectrograph for the 110 - 300 angstrom range. When the gradient was parallel to the TG lines, the TG was placed in the converging beam. When the gradient was orthogonal to the grating lines, the TG dispersed, unlike the configurations used previously, the diverging beam incident on the focusing MM. Removing the entrance slit transforms the spectrograph into a spectroheliograph. The latter configuration is well suited for producing 2-D solar images in the radiation of spectral lines and far-field images of single- and many- frequency x-ray lasers.