Abstract
During this thesis, we have used pulsating laser to generate and detect excitations inside n doped CdMnTe quantum well. The concentration in Mn in these quantum well is very low. We used the pump-probe technique to have acces to temporal domain of the excitations. We identifie spinwave of null wave-vector, and we try to caracterize them. We see that we excite and detect a new unexpected mode linked to the electron's spin of manganese. We developed a model which explain this new mode and give us acces to caracteristic of the 2d electrons gas : its polarization. The polarization is related to coulomb interactions in the electrons gas. We have compared or results to latest theories on the subject. Ours mesurements and our theorie are compatible with these theories and others mesurements done by others techniques.