A second optic head for the ELETTRA long trace profiler

The optical metrology laboratory of Elettra is equipped with some state of the art instruments for the characterization of high precision optical components for the UV and x-ray energy range. Among them, the most important is the Long Trace Profiler, which is capable of very accurate measurement of the shape of long aspheric mirrors. It is a direct slope measurement device, able to measure slope errors below the mrad level, once properly operated and calibrated. Our device is an LTP II model dating back to 1992. Nevertheless, it has been deeply in house modified during these years. Recently we have assembled a second optic head (OH) that could be used in spite of (or together with) the original one. This second OH works without folding mirrors and uses a set of short focal distance Fourier Transform lenses. The absence of folding mirrors reduces the source of systematic errors and the use of short focal distance lenses increases the angular acceptance of the instrument. This fact is particularly useful when short radius of curvature mirrors as well as high groove density variation gratings have to be measured. Some other modifications have been made to help the stitching procedure or to change the measurement set-up. These will be described in details.