In the new generation Extreme UltraViolet (EUV) lithography machines light with a wavelength of 13.5 nm is used for imaging. This very high energy light is absorbed by lenses, so mirrors are used instead. The mirrors can lose reflectivity due to different contaminating processes present in the machine. Two of these processes are the cracking of residual hydrocarbons and chemisorbed water by the EUV photons. The breaking of molecular bonds can create a non-volatile deposit of carbon and oxidize the surface.Ellipsometry is a powerful noninvasive optical technique for measuring the thickness and optical constants of thin films. Ellipsometry measures the polarization change after reflection on the surface of a sample. The polarization change can be related to sub nanometer thicknesses and makes it possible to measure layer growth in real-time.This research describes the development and calibration of an imaging ellipsometer. The main advantage for this setup lies in the in-situ spatially resolved measurements, not possible with traditional ellipsometers. This could provide new insides onto the contamination processes. Finally the setup will be used for measuring real-time electron beam induced carbon deposition and oxidation of metallic samples.