Broad-band stigmatic spectrograph for the soft x-ray range

We describe a panoramic stigmatic spectrograph comprising a grazing-incidence toroidal mirror and a large-aperture free-standing transmission diffraction grating (5000 lines mm^–1 ). Two spectrograph versions were constructed, with grazing angles of 7.6 and 4° and the short-wavelength spectral limits near 4 and 1.5 nm. The spectrograph aberrations were studied by numerical ray tracing. The spectrograph was used to record line and quasi-continuous spectra (1.5 — 30 nm) of multiply charged ions in a plasma generated by the second-harmonic pulses of an yttrium aluminate laser (Q = 0.15 J, τ = 5 ns, λ = 0.54 μm, repetition rate = 0.5 Hz). In combination with a laser-produced plasma radiation source, the arrangement was used to characterise soft x-ray optical components and to generate collimated beams of polarised radiation in the 14 — 20 nm range.