Thickness Determination of Transparent Coatings

Thickness determination of transparent objects or thick transparent layers can be carried out rather simpy using a chromatic confocal sensor. One obtains the thickness as the difference between two distance peaks multiplied with the refractive index of the object's material. A more detailed analysis however reveals that this result should be corrected by a factor that considers the refraction in detail. In this paper we derive and discuss this correction factor and give tabulated values for different refractive indices and aperture angles of the chromatic probe.