Thomas Hänsel

Advanced metrology: an essential support for the surface finishing of high performance x-ray optics

The performance of x-ray beamlines at 3rd generation synchrotron radiation sources and Free Electron Lasers (FELs) is limited by the quality of the state of the art optical elements. Proposed FEL beamlines require optical components which are of better quality than is available from the optical manufacturing technology of today. As a result of a joint research project (Nanometer Optik Komponenten - NOK) coordinated by BESSY, involving both metrologists and manufacturers it is possible now to manufacture optical components beyond the former limit of 0.1 arcsec rms slope error [1, 2]. To achieve the surface finishing of optical components with a slope error in the range of 0.04 arcsec rms (for flat or spherical surfaces up to 300 mm in length) by polishing and finally by ion beam figuring technology it is essential that the optical surface be mapped and the mapping data used as input for the multiple ion beam figuring stages. Metrology tools of at least five times superior accuracy to that required of the component have been developed in the course of the project. The Nanometer Optical Component measuring Machine (NOM) was developed at BESSY for line and area measurements of the figure of optical components used at grazing incidence in synchrotron radiation beamlines. Surfaces up to 730 cm2 have been measured with the NOM a measuring uncertainty in the range of 0.01 arcsec rms and a correspondingly high reproducibility [3]. Three dimensional measurements were used to correct polishing errors some nanometers high and only millimeters in lateral size by ion beam treatment. The design of the NOM, measurement results and results of NOM supported surface finishing by ion beam figuring will be discussed in detail. The improvement of beamline performance by the use of such high quality optical elements is demonstrated.

Ion beam figuring surface finishing of X-ray and synchrotron beam line optics using stitching interferometry for the surface topology measurement

Deterministic surface finishing using small-spot ion-beam figuring combined with stitching interferometry surface shape measurements for the enhanced lateral resolution have been developed to achieve 20marcsec slope-error on a 100mm flat Si synchrotron beam line optic.

Recent achievements on ion beam techniques for optics fabrication

The talk gives an overview on latest results on ion-beam technology development for optics fabrication: RIBE proportional transfer of 3-D micro- and nanostructures, smoothing down to the 0.1nm rms range and figuring below 0.5nm rms.