Basics of White-Light Interferometry

Interferometer Setup The Twyman–Green interferometer (Figure 1) is a special configuration of the well-known Michelson interferometer with optics that superimpose the images of the object and the reference planes. Polytec engineers use this interferometer and place a CCD image sensor like those used for digital photography at the point where the two images are superimposed. A broadband “white-light” source is used to illuminate the test and reference surfaces. A condenser lens collimates the light from the broadband light source. A beam splitter separates the light into reference and measurement beams. The reference beam is reflected by the reference mirror, while the measurement beam is reflected or scattered from the test surface. The returning beams are relayed by the beam splitter to the CCD image sensor, and form an interference pattern of the test surface topography that is spatially sampled by the individual CCD pixels. Vertically scanning white-light interferometry is a non-contact optical