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.
This presentation is a comparison of two technological methods used to test and qualify complex optical components: classical optical interferometry based on Fizeau interferometer and HASO TM Shack-Hartman metrology wavefront sensor with an auto-collimator and its focusing module. Shack-Hartman wavefront sensor consists in a microlens array mounted on a camera (CCD, CMOS, InGaAs sensors) at its focal length. The wavefront will be processed from an integration of all local slopes: the local slopes of the wavefront are calculated by measuring the position of each spot from sub-pupil on the camera. We integrate this metrology wavefront sensor on an optical platform including an auto-collimator (laser diode wavelength to be chosen in the 400 nm to 1100 nm range), a beam-splitter and a focusing module (to be optimised depending on application) so that the system is divergent and can adjust to any optical components size. This system can thus be used on large concave mirror in single pass configuration (standard accuracy of λ/100rms) or transmission optics in double-pass configurations. We will show aberrations cartography of several complex components (biconvex lens, telescope mirror for instance) measured with both technologies, which are fully consistent with Zemax optical simulations software. A big advantage of Shack-Hartman principle is vibration insensitivity, contrary to interferometry. We will emphasize on pros and cons from each technology: wavelength range, chromaticity, price, dimensions, resolution, sensitivity, repeatability, reliability.
The push for high quality x-ray optics is closely linked to improvements in metrology technology. During the last decade, we have seen an ultra-fast progress in x-ray optics performances. This enhancement is directly linked to the development of the necessary tools to control these optical components. These metrology tools are necessary for the fabrication (to guide some polishing deterministic process) and also for the ultimate characterization used to validate surface parameters (often inside their own mechanical support) prior to installation in a beam line. It is now necessary to characterize optical surface figure, slope errors and roughness on meter-long optics over spatial frequencies as short as 0.1 mm and with slope errors reaching less than 100 nrad rms or surface figure errors close to 1 nm in order to not spoiled and preserve the high brightness made available by third and fourth generation synchrotron/FEL sources like NSLSII or LCLS. For this purpose, the new NSLS-II Optical Metrology Laboratory (NSLSII-OML) includes commercial instruments for measuring long spatial frequency figure errors, mid spatial frequencies and high frequency roughness and had started some research and development activities. This paper provides a brief description of the instruments currently available in the laboratory and gives an overview of the very active research and development efforts within the NSLSII-OML.
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