Traditional optical manufacturing methods employing both conventional and modern interferometric techniques, enable one to measure surface deviations to high accuracy, e.g. up to lambda/100 for flats (6 nm P-V). In synchrotron radiation applications the slope error is an important criterion for the qualify of optical surfaces. In order to predict the performance of a synchrotron radiation mirror the slope errors of the surface must be known. Up to now, the highest achievable accuracy in the production of synchrotron radiation mirrors and in the measuring methods did not fall significantly below the 0.1 arcsec rms limit (spherical and flat surfaces). A long-trace profiler (LTP) is ideally suited for this task since it directly measures slope deviations with high precision. Ore the other hand, using an LTP becomes very sensitive to random and systematic errors at the limit of 0.1 arcsec. The main influence is the variation of the surrounding temperature in creating temporal and local temperature gradients at the instrument. At BESSY both temperature and vibrations are monitored at the most sensitve points of the LTP. In 1996 BESSY started a collaboration with a neighboring optical workshop combining traditional. manufacturing technology with quasi-in-process high precision LTP measurements. As result of this mutual polishing and LTP measuring process, flat surfaces have been repeatedly produced with shope errors of 0.05 arcsec rms, e.g. 1 nm pms and 3 nm P-V (approximate to lambda/200).
