Synchrotron and Free Electron Laser beamlines new needs require the use of mirrors and gratings with less than 50 nrad rms slope error and less than 1nm height error to reach the diffraction limit at the user wavelength and at the right angle of incidence. In order to manufacture such mirrors and gratings, some new metrology tools have been developed based on beam deflection or interferometry.
The new concept of SHARPeR relies on an optical head including a collimator in visible light, a beam expander to image the mirror on a very sensitive Shack-Hartmann wavefront sensor. This optical head is set on a granite table on which the mirror is set and aligned. Some wavefront measurements are acquired as the head is translated among the mirror surface. A stitching algorithm is then used to calculate the mirror height from the small raw data maps while removing the stage defects by analyzing the overlapped areas.
Multiple scans have been acquired on the same mirror to evaluate the system sensitivity depending on the external environment (temperature stabilization, air turbulences...). We'll discuss some comparisons done with measurements obtained on some other instruments to conclude on the proven accuracy of this system.
With a spatial resolution of 1.2mm, a proven accuracy of less than 100 nrad rms (0.8 nm rms in height) on a 300mm long mirror, with the capability of measuring 1.5m long mirror in less than 30 minutes, SHARPeR has become a new solution for extreme metrology of XRays mirrors.
Guillaume Dovillaire and Rafael Mayer, "SHARPeR: a non contact 2D profiling instrument at the nanoradian scale (Conference Presentation)," Proc. SPIE 10539, Photonic Instrumentation Engineering V, 105390U (Presented at SPIE OPTO: February 01, 2018; Published: 14 March 2018); https://doi.org/10.1117/12.2289882.5751517315001.
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