A confocal setup based on microlenses for shape investigation, defect analysis and surface topography measurement is presented. The major advantage of this technique is its high light efficiency and the possibility to realize larger object fields without reducing the numerical aperture. Different variations of the setup for different applications are presented. An increased working distance yields a greater variety of its applications. Furthermore, the arrangement of the microlenses on a rotating disk leads to an increased spatial sampling and a high scanning rate. The axial resolution is the same as in a comparable confocal microscope based on a Nipkow disk. The microlens confocal system enables measurements on large field sizes down to microscopic ones. In addition, by using chromatic aberrations it is possible to achieve realtime images with color-coded height information. The topography of the sample can be determined from one color image, which leads to a reduction in measuring time. To reduce measuring times on curved surfaces, for instance, it is useful to adapt the focal lengths of the microlenses to the individual shape of the object. Hence, only the difference between the focal distribution and the real shape must be determined.
Hans J. Tiziani,
"Confocal principle for macro- and microscopic surface and defect analysis," Optical Engineering 39(1), (1 January 2000). http://dx.doi.org/10.1117/1.602332