OPTICAL MONITORING SYSTEM FOR COATING PROCESSES

The invention relates to an optical monitoring system for measuring the thickness of thin layers that are applied in a vacuum, especially on moved substrates during the coating process. In said optical monitoring system, the intensity of the light of a light source which is injected into a reference light circuit and is transmitted by a first piezoelectric or electrostrictive or magnetostrictive light chopper is detected by a light detector unit in a reference phase, the light of said light source is injected into a first measuring light circuit in a measuring phase, the light transmitted by a second piezoelectric or electrostrictive or magnetostrictive light chopper is directed onto the substrate, the intensity of the light reflected or transmitted by the substrate is detected by the light detector unit via a second measuring light circuit, and the intensity of the remaining light is detected by the light detector unit in at least one dark phase. The reference phase, the measuring phase, and the dark phase are digitally adjusted in an offset manner and in accordance with the position of the substrate via the light choppers.