Mandrel replication by NiCo electroforming is an upgrade of the well-suited X-ray mirrors manufacturing process with
pure Nickel. In this process, a Gold layer deposited on the mandrel acts as release agent and, at the same time, as
reflective coating. To increase the optical performances of X-ray mirrors, the replicated optical surface is meant to
reproduce the smooth topography of the mandrel: a surface degradation is commonly observed, indeed. A factor leading
to surface smoothness worsening can be the spontaneous roughness growth of the Gold layer itself; therefore, the optical
quality of the reflecting surface might be improved by optimizing the Gold layer thickness. A preliminary study, aimed
at investigating the effects of Gold thickness reduction (< 100 nm Vs. the usual 200 nm), had already been dealt in the
spectral range 0.02-1000 μm: measurements performed on flat electroformed samples showed that the Gold thickness
reduction chiefly affects the roughness around 1 μm. Here we presents a study of the effectiveness of a Gold layer with
reduced (< 100 nm) thickness in the NiCo X-ray mirrors electroforming, aimed at surface micro-roughness mitigation.
The characterization, in the spectral range 0.02-1000 μm, of 3 X-ray mirrors manufactured utilizing Gold layers with
different thickness values from a flight mandrel is reported. The performed investigation is organized as follows: (a)
characterization of the flight mandrel; (b) dependence of the micro-roughness from different Gold layers thicknesses
supported by XRD study; (c) comparison of the micro-roughness of mirrors manufactured in NiCo in Ni, with the same
Gold layer thickness. As a conclusive remark the effects of the Gold layer thinning on the angular degradation at high
energy are reported.