Coating system and methods for cleaning an optical sensor of the coating system

Coating system for depositing a layer on a substrate with an optical sensor (1) for receiving optical signals in the coating system, comprising an optical receiver (2) for receiving an optical signal, and having a device for generating a planar distributed, on the substrate directed gas stream to control the temperature of the substrate, characterized in that a partial stream of the serving of Substrattemperierung gas stream is branched off and that the optical receiver (2) is assigned a nozzle (8), which in such a way with the means for generating the directed at the substrate gas stream communicating that said partial flow as a gas flow (10) is to be directed to the optical receiver (2) by means of the nozzle (8).