Test in liquid argon of the light readout system for the ArDM experiment

ArDM is a new-generation WIMP detector which will measure simultaneously light and charge from scintillation and ionization of liquid argon. Our goal is to construct, characterize and operate a 1 ton liquid argon (LAr) underground detector. The project relies on the possibility to read out the VUV scintillation light and to extract the electrons produced by ionization from the liquid into the gas phase of the detector, to amplify and read out with Large Electron Multipliers detectors. The light has to be converted with wavelength shifters such as TetraPhenyl Butadiene in order to be detected by photomultipliers with bialkali photocathodes. I'll describe the light readout system R&D and report about the tests and the calibration of the prototype with liquid argon in the full size detector.