Measurements of reflection spectra of soft X-ray multilayer mirrors using a broadband laser-plasma radiation source

The reflection spectra of several concave (spherical and parabolic) periodic Mo/Si, Mg/Si, and Al/Zr multilayer mirrors intended for cosmic experiments were studied with the help of a laser-plasma soft X-ray radiation source. An investigation was made of the reflection spectra of a laboratory aperiodic Mo/Si multilayer mirror optimised for maximum uniform reflectivity in the 125—250-Å range. 'Satellites' were observed in the neighbourhood of the principal peak in the spectrum of the periodic 132-Å multilayer mirror. High-intensity second-order interference reflection peaks at wavelengths of about 160 Å were experimentally revealed in the reflection spectra of the periodic Mo/Si 304-Å mirrors. By contrast, the second-order reflection peak is substantially depressed in the spectra of the narrow-band mirrors based on the Mg/Si multilayer structure. The experimental data are compared with theoretical calculations. Manifestations of the NEXAFS structure of the L_2,3 absorption edges of Al and Al₂O₃ were observed in the spectra recorded.