White-light interference is an optical phenomenon resulting from two broadband light rays [e.g. from a halogen lamp] interfering with one another. The interference pattern varies with respect to the phase difference of the 2 [or more] waves where parts of the light are periodically attenuated or amplified.
This phenomenon can be utilized to measure the thickness of transparent layers. The interference occurs at the optical boundaries of the transparent layers where a certain amount of light is reflected. Different layer thicknesses induce varying phase differences of the back-scattered light. This can be used to evaluate the layer thickness by analyzing the interference spectrum. Depending on the spectral sensor, a layer thickness of 0.1 to 150 µm can be detected with high reproducibility using a special Fourier analysis.