In the new surface laboratory the 3D surface topography of a specimen can be measured by using a white-light confocal microscope. Confocal microscopy works by a point distance measurement using a depth discrimination method in reflection mode. In a first focusing step light which is emitted from a point source is imaged into the object focal plane of a microscope objective. An in-focus specimen location results in a maximum flux of the reflected light through a detector pinhole (second focusing), whereas light from defocused object regions is partly suppressed. Therefore, the detector signal, as limited by the pinhole size, is reduced drastically when defocusing the specimen. For the current laboratory equipment this principal design was improved for fast 3D measurements by use of a spinning multiple pinhole mast (Nipkow disk) in an intermediate image plane of a microscope. The Nipkow-disk consists of an array of pinholes arranged in a spiral shape. The disk which is operated in a spinning mode is illuminated by a plane wave and acts as a scanning multiple point light source which is imaged into the object focal plane of the microscope objective. After the reflection of light each illuminating Nipkow pinhole acts as its own detector pinhole. Combined with fast CCD image processing the rotating Nipkow disk affects the in-plane-scan of the object field in video-real-time. Therefore, only the additional out-of-plane scan is required for 3D acquisition. The Nipkow-disk expands the effect of depth discrimination to the area of the microscope object field, which allows optical sectioning like in computer tomography.
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