Simplified schematic of slope measurements with the ALS DLTP instrument. The optical slope sensor of the DLTP is a high-precision autocollimator. In the course of a measurement, scanning along a SUT is performed by translating a pentaprism in the forward (increase in the coordinate) or backward direction.
Suppression of the exponential drift described by Eq. (41) with the parameters and . (a) Time dependence of the exponential drift. (b) The same drift is presented as a dependence on the spatial position along a SUT when four scans are performed according to the scan strategy . (c) The resulting traces of the slope error due to the exponential drift measured in four successive scans performed in one direction (blue line and points) and in four scans performed according to the optimal scanning strategy (red line and points).
(a) DLTP setup drift as a difference of the slope traces measured in the first (1st) and the last (16th) scans of the measurement series #199 (see text). The number of the series, #199, relates to a current number of the measurement series when it was performed with the DLTP. (b) Difference of the last scan of the same measured series #199 and the resulting trace averaged over all six measurement series. (c) Half of the difference of the measurements performed with the mirror with the direct and reversed orientations.
The red points and line are DLTP measurements with the S3 reference mirror. The blue points and line present the residual slope trace obtained with BESSY NOM (courtesy of Frank Siewert).
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