An Optical profiler like The ProFilm3D are used to measure surface height variations such as surface roughness and topography on a wide variety of surfaces with very high levels of precision that use the wavelength of light as their ruler. The systems utilise optical interference profiling which is a well-established method of obtaining accurate surface topography and interfacial layer thickness measurements.
Inside an optical interference profiler, a light beam is split, reflecting half the beam from a test material which is passed through the focal plane of a microscope objective lens, and the other half of the split beam is reflected from the reference mirror.
When the distance from the beam splitter to the reference mirror is the same distance as the beam splitter is from the test surface and the split beams are recombined, constructive and destructive interference occurs in the combined beam wherever the length of the light beams vary. This creates the light and dark bands known as interference fringes.
Since the reference mirror is of a known flatness-that is, it is as close to perfect flatness as possible-the optical path differences are due to height variances in the test surface.