Modelisation of Light Transmission through Surfaces with Thin Film Optical Coating in Geant4

Surfaces with optical coating may be used to improve light transmission between a scintillating crystal and a photodetector. For the ClearMind project, we develop a detection module made of a PbWO
4
crystal and a photocathode directly deposited on a thin passivation film coating the crystal face. Scintillation photons will then be transmitted through this thin film that has a thickness of the order of the scintillation light wavelength. Interference phenomena and frustrated transmission beyond the limit angle have then to be considered. We present the modelisation of light transmission through surfaces with optical coating with Geant4, which is achieved by defining a new method that provides a probability of transmission of a visible-UV photons through the coated interface