Abstract
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.
