Argon ion beam sputtering is used for production of high-quality Mo/Si multilayer Bragg mirrors with 13.4 nm center peak wavelength. The growth of the layer system was monitored in situ by real-time ellipsometry at multiple wavelengths within the visible to ultraviolet spectral region. The layer thicknesses of the individual multilayer constituents are obtained by model analysis of the ellipsometry data. Quality and performance of the soft x-ray mirrors is demonstrated by transmission electron microscopy, atomic force microscopy, glancing-angle of incidence Cu Kα reflectivity, and near-normal incidence soft x-ray reflectivity measurements. Thickness values obtained by transmission electron microscopy, reflectometry, and ellipsometry are critically compared.