Fehérfényinterferometriai

Fehérfényinterferometriai, or white light interferometry, is an optical technique used to measure surface topography and surface roughness. It utilizes the interference of light waves to create fringe patterns that are directly related to the height variations of a sample. Unlike monochromatic interferometry, which uses light of a single wavelength, white light interferometry employs a broadband light source, typically a halogen lamp or a white LED. This broadband source has a very short coherence length.

The principle of white light interferometry relies on the fact that interference fringes are only visible when the optical path difference between the two interfering beams is within the coherence length of the light source. In a typical setup, white light is split into a reference beam and a sample beam. The sample beam is reflected off the surface of the object being measured, while the reference beam is reflected off a reference mirror. When these beams are recombined, they interfere.

Because the white light has a short coherence length, interference fringes are only observed when the optical path difference between the sample surface and the reference mirror is very small, effectively close to zero. As the sample is scanned vertically, or the reference mirror is moved, the detector records the intensity of the recombined light. Peaks in intensity indicate constructive interference, occurring when the path difference is an integer multiple of the wavelength. However, due to the broadband nature of white light, only the central fringe, corresponding to zero path difference, is bright and distinct. This allows for unambiguous determination of the surface height. By analyzing the position of this central fringe as a function of lateral position on the sample, a three-dimensional topographical map of the surface can be reconstructed. This technique is non-contact and can achieve very high vertical resolutions, making it suitable for inspecting a wide range of surfaces in industries such as semiconductor manufacturing, optics, and precision engineering.