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Proceedings Paper

Micro Fabry-Perot sensor for surface measurement
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Paper Abstract

A high accuracy surface inspection system for testing polished surfaces is based on a Fabry-Perot resonator. The inspected surface serves as a relay mirror in a cat-eye retroreflector incorporated into the resonating cavity, which makes the optical configuration insensitive to surface tilts. The laser wavelength is swept periodically over a given range, and the local surface height is obtained by timing the resonance occurrence during each sweep. An additional highly stable reference Fabry-Perot interferometer using the same laser is employed for obtaining differential measurements, yielding absolute height values, distinguishing between up and down defects. Due to the finesse of the multi-beam Fabry Perot interferometer relative to the two-beam Michelson interferometer response function, the height sensitivity is greatly enhanced. In order to detect small contamination particles, the interferometer was supplemented by a scattering detection channel integrated into the same compact optical head. The combination of the bright-field interferometric signal, yielding both the phase (surface height) and amplitude (surface reflectivity), and the dark-field scattering channel, allows one to build a sensitive and reliable defect detection and classification procedure. The interferometer was incorporated into high-speed high-accuracy in-line machines for inspection of the surfaces in data storage applications. With a 0.2 Angstroms resolution, the height rms repeatability at a surface scanning speed of 40 m/s is 1.5 Angstroms.

Paper Details

Date Published: 11 August 2008
PDF: 12 pages
Proc. SPIE 7063, Interferometry XIV: Techniques and Analysis, 70630U (11 August 2008); doi: 10.1117/12.798135
Show Author Affiliations
Andrei Brunfeld, Xyratex International Inc. (United States)
Gregory Toker, Xyratex International Inc. (United States)
Morey T. Roscrow Jr., Xyratex International Inc. (United States)
Bryan Clark, Xyratex International Inc. (United States)

Published in SPIE Proceedings Vol. 7063:
Interferometry XIV: Techniques and Analysis
Joanna Schmit; Katherine Creath; Catherine E. Towers, Editor(s)

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