This manuscript deals with the topic of time-resolved magneto-optical properties of Au/Co/Au. The temporal resolution is sub-picosecond and the layer of cobalt is ultrathin (several atomic-layer thick). During this work, we built an experimental set-up of two-color pump-probe measurements which required the confection of a femtosecond optical source (OPA). Double-demodulation techniques provided the dynamical magneto-optical response of the system. Within the investigated spectral range, the Au/Co/Au system can be considered as a hybrid material as far as its non-linear magneto-optical properties are concerned : the temporal evolutions of transmission and reflection spectra are due to the dielectric constant of gold. The temporal evolutions of the complex Kerr rotation spectra can be mainly put on the account of the non-diagonal term of the dielectric tensor of cobalt. We demonstrated that the ultrathin cobalt layer deeply fastens the relaxation of the electronic gas in the multilayer system in comparison with the one in a gold layer. As regards to the magnetization relaxation, we noticed that no direct relation between the magnetization and the optical measurements exists in this ultra-fast regime. No instantaneous demagnetization in our system has been observed because of several agneto-optical effects that we discussed.
