The paraboloidal mirror

The focal spot of the X-ray source is placed in the focus of a paraboloidal mirror (4750 mm focal length). Upon reflection onto the paraboloidal mirror, the beam becomes parallel. The focal distance, combined to a source size of 35 µm FWHM, yields a final beam divergence of nearly 1 arcsec.
The mirror was polished and figured at INAF-OABrera, starting from a fused quartz substrate pre-formed in a preliminary lapping state by Zeiss (Oberkochen, Germany).
A Zeeko IRP 1200 machine has been used to remove the surface damage from the mirror as procured and to reduce the surface roughness within a specific tolerance. Our IBF machine has been subsequently used to correct the mirror shape. The performance of each polishing/figuring run has been monitored using the MPR and CCI metrology tools available at Media Lario (Bosisio Parini, Italy). After oncoming tests at PANTER (MPE), the mirror was coated with a platinum layer at DTU to enhance its reflectivity at 4.5 keV. The alignment of the mirror to the X-ray source was achieved with a Micro Alignment Telescope, a Laser Tracker, and an Hartmann plate procured with ad hoc design.