Paradigm of the time-resolved magneto-optical Kerr effect for femtosecond magnetism

摘要: Conventional understanding of the magneto-optical Kerr effect, in which changes magnetization a material cause polarization reflected light, assumes that this incident light is continuous. However, first-principles simulations nickel show assumption breaks down for femtosecond pulses and establishes firm foundation dynamics femtomagnetism. The effect (MOKE) powerful tool studying ferromagnetic materials. It works by measuring light. because conventional theoretical basis interpreting MOKE signal measurement with continuous-wave light1,2, its use high-speed probed optical pulses3,4 has been controversial5,6,7,8,9,10. Here we establish new paradigm time-resolved measurements, through investigation nickel. We magnetic responses energetically follow their respective susceptibilities. As result, one-to-one correspondence between them sensitively depends on photon energy. In nickel, energies below 2 eV response faithfully response, but above they decouple. By constructing phase-sensitive versus plot, find short signals are delayed 10 fs respect to signals. For longer pulses, delay shortens behaviour approaches response. This finally resolves long-standing dispute over interpretation measurements lays solid femtomagnetism3,4.