Riedel, W.J.W.J.RiedelGrisar, R.R.GrisarWölfelschneider, H.H.Wölfelschneider2022-03-082022-03-081997https://publica.fraunhofer.de/handle/publica/303812In a device for the measurement of coating thicknesses based on white light interferometry, the output light (2) of a broadband light source (1) can be focused within a focal range (35) onto the object under test (37) by means of a focussing unit (7). By changing the optical path length in an object arm (19) by means of a beam deflection device (24), a focal range (35) can be shifted via bounding surfaces (36, 38, 39, 40) of the object (37). Interference signals can be produced with a high contrast and a high signal-to-noise ratio by time coherence and spatial superposition of the wave fronts curved by focussing the light component (18) back-reflected in the object arm (19) with a light component (15) passing though a reference arm (14). The position of the interference signals in relation to the shifting of the beam deflection device (24) can be evaluated by an evaluating unit which consists of a voltage-controlled oscillator and a phase-independent synchronizing rectifier. The coatin g thicknesses result from determining the distance between the interference signal maxima in relation to oscillation periods of the voltage-controlled oscillator controlled by the signal proportional to the shift velocity.de608621patent1994-4425178