Room-temperature study of ultrafast spin dynamics in bulk semiconductors by the photo-induced magneto-optical Kerr effect

The room-temperature dynamics of spins in bulk GaAs and CdTe is investigated using the time-resolved, pump and probe, photo-induced, near-resonant magneto-optical Kerr effect. Three components with different temporal and spectral behaviors are found and their origins discussed in relation with theoretical predictions. Two contributions are attributed to the spin-dependent splitting of the energy sub-levels. The first one, present only when pump and probe pulses coexist, is accounted for in terms of the optical Stark effect, whereas the longer decay of the second one, up to a few tens of ps, is attributed to electron spin relaxation. The third component, assumed to arise from the difference in population of the photo-excited states, decays within less than 50 fs, which is attributed to the energy relaxation of electrons towards the bottom of the conduction band through scattering processes.