| Terahertz (THz) Emission Spectroscopy (TES) has emerged as a powerful technique to study time-dependent changes in polarization, current, and magnetization. The defining attributes of TES are phase-sensitive detection, which allows the directionality of these processes to be determined, and a signal strength that is directly produced by the process of interest. Other techniques indirectly monitor these processes through changes in related optical transitions.;The polarization dependence of terahertz emission from optical rectification and shift currents in GaAs is studied using TES. The dependence of optical rectification and shift currents generated by excitation far above the band gap agrees closely with theoretical calculations. When exciting slightly above the band gap, the linear polarization dependence agrees with theoretical calculations, but the elliptical polarization dependence yields results that vary substantially from the calculations. We attribute this variation to the generation of spin-polarized electrons that create a magnetic field within the sample. This field alters the direction of the electrical current containing these same electrons via the Hall effect.;Additionally, TES is used to extract the sub-ps dynamics from the ultrafast laser-induced demagnetization in thin magnetic films. In Fe and Ni thin films, the THz emission is strongly dependent on the thickness of the sample where the thicker films (30--60 nm) behave in a way consistent with bulk demagnetization and the thinner samples (5--15 nm) exhibit behavior that is dominated by a surface response. The emission caused by bulk demagnetization in Ni films is fit to a phenomenological model that finds the electron thermalization time, &tgr;e, to be 370 fs and electron-phonon interaction time, &tgr;eph, to be 1.3 ps, which are consistent with previous findings. The bulk demagnetization dynamics in Fe are substantially different, with the full remanent magnetization regained within 2 ps, compared with only 30% magnetization regained in Ni on the same timescale. |
