| Ferromagnetic film is important for information industry, and it is very important to study the spin dynamics of ferromagnetic film for improving their application. It is showed in spin dynamics study that the spin evolves in terahertz range. The building of time resolved terahertz measurement experimental setup is detailedly introduced in this thesis. The terahertz radiation from the interaction between femtosecond laser pulse and Fe/Pt heterostructure films were investigated with this setup.In our measurement, we found that the amplitude, spectra and polarization of the terahertz radiation is independent of the polarization of the femtosecond laser pulse, and the amplitude is proportional to the power of laser pulse, which indicates that the terahertz radiation is related to the hot electron(instead of coherent electron) excited by laser pulse.The terahertz radiation decays exponentially with the increase of Fe or Pt thickness, the decaying constant were obtained by analyzing the experimental data, which is consisted with the Drude model calculation.The amplitude of the THz radiation has a certain hysteresis effect when it responses to the external magnetic field, which is similar to the hysteresis loop of VSM data. Since the time resolved THz wave curves in experiments is very similar to the second derivative of the time resolved MOKE data, we attribute that the THz radiation is resulted from the demagnetization from femtosecond laser excitation of ferromagnetic film, and the change of the magnetic field in the demagnetization process is influenced by various effects. |
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