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15 October 2012 Cross comparison of surface slope and height optical metrology with a super-polished plane Si mirror
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We report on a cross-comparison of low-spatial-frequency surface slope and height metrology with a super-polished flat X-ray mirror Si substrate fabricated for the Stanford Linear Accelerator Center Linac Coherent Light Source hard X-ray mirror system HOMS-3. The substrate with overall dimensions of 450 × 30 × 50 mm3 was specified to have a radius of curvature between 150 km and 195 km with a residual (after subtraction of the best-fit cylinder) slope variation on the level of 0.1 μrad rms, when measured in the tangential direction over a clear aperture of 380 × 5 mm2. Surface slope metrology with an accuracy of better than 60 nrad rms was performed with an upgraded long trace profiler LTP-II and an auto-collimator-based developmental LTP (DLTP). The instruments are available at Advanced Light Source optical metrology laboratory. Surface figure in the height domain was characterized at the Lawrence Livermore National Laboratory X-ray science and technology group with a large field-of-view ZYGOTM (12 in) interferometer. The error of the interferometric measurement is estimated to be approximately 0.5 nm rms. We describe in detail the experimental methods and techniques that achieved state-of-the-art metrology with the super-high quality optic under test. We also discuss the relation between surface slope and height metrology and the principle problems of their cross-comparison. We show that with some precautions cross comparison can be made reliably, providing supplemental information on urface figure quality.
© (2012) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Nikolay A. Artemiev, Daniel J. Merthe, Daniele Cocco, Nicholas Kelez, Thomas J. McCarville, Michael J. Pivovaroff, David W. Rich, James L. Turner, Wayne R. McKinney, and Valeriy V. Yashchuk "Cross comparison of surface slope and height optical metrology with a super-polished plane Si mirror", Proc. SPIE 8501, Advances in Metrology for X-Ray and EUV Optics IV, 850105 (15 October 2012);

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