From Event: SPIE Optical Engineering + Applications, 2016
We present the continuous scan operation of the ALBA-NOM as a working mode that allows obtaining low noise in
short time, as well as high accuracy measurements. In the traditional step-scan operation, the position of the probe beam
is kept fixed while many data points of autocollimator are averaged for noise reduction. This operation mode is very
safe, as one has a perfect correspondence between mirror position and measured angle, but it is time inefficient, as it
disregards all the data values acquired during motion, and basically averages data values taken under identical
conditions. On the other hand, continuous scan is less safe in terms of correspondence between mirror position and slope,
especially for NOM systems for which the autocollimator does not accept an electronic trigger. Nevertheless, it is
possible to perform independent acquisitions of the autocollimator and of the linear stage data during a scan, and
synchronize signals a posteriori. This solves the main problem of continuous scan with a NOM. Continuous scan
operation for performing measurements is very efficient for noise reduction per unit time, as it allows integrating every
single data value taken by the autocollimator. In addition, it opens the possibility of introducing pitch variations of the
mirror between scans. This allows obtaining many independent datasets that can be combined using error suppression
techniques to reduce not just noise but systematic errors too. In this paper we report the methods and the main results.
Josep Nicolas, Pablo Pedreira, Igors Šics, Claudio Ramírez, and Juan Campos, "Nanometer accuracy with continuous scans at the ALBA-NOM," Proc. SPIE 9962, Advances in Metrology for X-Ray and EUV Optics VI, 996203 (Presented at SPIE Optical Engineering + Applications: August 29, 2016; Published: 8 September 2016); https://doi.org/10.1117/12.2238128.
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