FLIMM and TSM: two thermal methods for space charges investigation

For the measurement of space charges profiles, various experimental techniques are available, the most known being the thermal and the acoustic methods. The methods we use for the determination of the space charges belong to the group of non-destructive thermal methods, called FLIMM (Focused Laser Intensity Modulation Method) and TSM (Thermal Step Method). These thermal methods are based on the interaction between the thermal wave and the electric charges present in the insulator, which generates a pyroelectric current. Their thermal excitation process are different: the FLIMM method uses a laser beam modulated in intensity, on the other hand, the TSM method rests on the creation of a thermal step on one side of the sample. Knowing the pyroelectric current and the temperature profile, and using an appropriate mathematical deconvolution, the space charges distribution can be determined. In this paper, after detailing the principle of these two techniques, one will present the space charges profiles obtained for PET (polyethylene terephthalate) samples conditioned at different temperatures and electric fields.