3D cartography of space charges induced by UV irradiation

UV irradiation produces irreversible damages in the dielectric insulators. Irradiation sources are numerous: partial discharges, parasitic discharges (environmental) or ambient light. The most known effect of irradiation is yellowing indicating an advanced material damage. We already have shown that before yellowing, space charges appear close to the irradiated surface, and increase with the irradiation time. In order to investigate more precisely this phenomenon, electroluminescence measurements and space charges detection were undertaken. For space charge measurements, the FLIMM (Focused Laser Intensity Modulation Method) technique was used. This non destructive method allows localized charges detection and also the carrying out of 3D cartographies with a very good spatial resolution. The studied material was 25 mum thick Poly(ethylene 2.6-naphthalate) (PEN). During the irradiation, the samples were protected by a mask, except a small circular area (D = 4 mm). In this paper, three-dimensional space charges and global electroluminescence (EL) and intensity profiles are shown. The discussion deals with the UV induced modification by studying the difference between the level signal in irradiated zone and a non irradiated one, and the performances of the detection techniques in terms of accuracy.