Bragg mirrors with superlattices and depth grading of their period are studied
numerically at sub-10-nm wavelengths, using La/B4C and Cr/Sc as bilayer materials at 6.64 and
3.12 nm, respectively. Superlattice-related reflection peaks (between normal incidence and total
reflection) are very narrow, and sharpen with decreasing wavelength. Depth grading reduces
and broadens the peaks. Together with weighting by source spectra, all-angle reflection is
demonstrated. For the normal-incidence peaks, grading and weighting increases their overlap
with source spectra and allows enhancement of the total collected power by up to 120% (at
6.64 nm) and 90% (3.12 nm) compared to ungraded mirrors. Interface roughness, determined
from experimental data, approximately halves these enhancements.