Confocal scanning is a microscopy imaging technique that utilizes an aperture at the confocal plane of the objective. Out-of-focus light is thus prevented from entering the imaging system and only the in-focus plane on the sample is captured. 2D and 3D surface images can be captured by scanning the aperture mechanically or digitally.
Optical interferometry makes use of the optical path difference between light reflected in the two arms of the interferometer (reference and sample) to yield an spatial interference pattern (interferograms) that contains information on the surface topology of the sample. Various variations of the approach can be used for particular applications.
Focus Variation vertically scans either optics (with very low depth-of-field) or the sample to obtain a continuous set of images of the surface. An algorithm determines which points in each frame are in focus, and an entire image is built up using all in-focus points from all frames.
Spectroscopic Reflectometry reflects white light off of a single or multilayer thin film. All reflections from each interface within the layer structure are superposed coherently, creating a complex interference pattern. Analyzing this pattern over a range of different wavelengths present.