Spectral characterisation of aperiodic normal-incidence Sb/B₄C multilayer mirrors for the λ < 124 Å range

Three broadband aperiodic Sb/B₄C multilayer mirrors were synthesised for the purposes of soft X-ray optics and spectroscopy in the wavelength range beyond the L-edge of Si (λ < 124 Å), and their reflection spectra were measured. The multilayer structures were optimised for maximum uniform reflectivity in the ranges 100 – 120 Å, 95 – 105 Å and 90 – 100 Å. The reflection spectra were recorded using a laboratory laser-plasma radiation source and an electronic detector with a 2D spatial resolution (a CCD matrix with 13 × 13 μm sized pixels). The experimental spectra are compared with theoretical calculations. The effect of lower antimony and B₄C layer densities on the reflection spectra is discussed. (invited paper)