Confocal versus interference microscopy: 3D resolution analysis

Confocal and interference microscopy are the two most widely used optical techniques for surface topography measurement. Nonetheless, due to diffraction effects, which are inevitable in optical far-field measurement methods, both techniques are limited in their lateral resolution. In contrast to conventional microscopes, where the lateral resolution is usually defined by a single number such as the Abbe limit, a more comprehensive (3D) characterization of resolution is required for surface topography measurement. The instrument transfer function (ITF) provides the height response of a profiler as a function of the surface's lateral spatial frequency content assuming linear systems theory. Comparing numerically calculated ITFs, we outline that interference microscopy can outperform confocal microscopy in terms of both, lateral and axial resolution, provided that appropriate signal processing is being used.