Coherent spin dynamics induced by femtosecond pulses in ferromagnets

According to the fundamental equations of the relativistic quantum electrodynamics (QED) describing the light matter interaction, a femtosecond laser pulse can instantaneously modify the spin dynamics in a ferromagnetic material. It is this physical phenomenon that precedes the laser induced demagnetization occuring at the femtosecond time scale, that we have investigated using femtosecond optical pulses [1].