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Optical metrology

Non-contact measurement of aspherical and freeform optics with a new confocal tracking profiler

Optical metrology
Agusti Pinto
R&D Engineering Manager, Ph.D. in Physics at Sensofar Medical

In 2003 Agustí was awarded a Fulbright scholarship to carry out research on phasing of large segmented telescopes at the University of California, Irvine.
His research interests include optical metrology and phasing of large segmented telescopes and confer the Sensofar R&D group an outstanding position to always stay up-to-date in terms of innovation and the highest technological level.

Non-contact measurement of aspherical and freeform optics with a new confocal tracking profiler full article
Agustí Pintó1, Ferran Laguarta2, Roger Artigas2, Cristina Cadevall2
1Sensofar-Tech, S.L. (Spain)
2Universitat Politècnica de Catalunya (UPC) Rambla Sant Nebridi, 10, E-08222 Terrassa, Spain

Proceedings Volume 8169, Optical Fabrication, Testing, and Metrology IV; 81690V (2011)
Event: SPIE Optical Systems Design, 2011, Marseille, France


In this paper we introduce a new optical technique for the measurement of aspheric and free-form optics and moulds. This technique, called confocal tracking, consists on tracking the focus on the sample while it is moved along the horizontal XY axes. Unlike all single-point based techniques, confocal tracking images the surface, which makes it possible to determine the best in focus position within every field of view and to correct the residual tracking errors for each measured point.

As a result, confocal tracking provides shape measurements with nm-level accuracy and acquisition speeds of 1 mm/s typically. Depending on sample geometry, high NA objectives can be used, with which it is possible to measure slopes as high as 65°. In addition, because confocal tracking is not a single-point but an imaging technique, it is possible to center the surface to be measured with a very quick procedure that can be automated easily. This step may be particularly relevant for optics with symmetry of revolution.

The confocal tracking profiler is a proprietary technology of UPC and Sensofar and can be considered the optical equivalent of a high-accuracy contact profiler.

Three-dimensional measurements