The femtosecond magnetization dynamics of a thin cobalt film excited with ultrashort laser pulses has been studied using two complementary pump-probe techniques, namely spin-, energyand time-resolved photoemission and time-resolved magneto-optical Kerr effect. Combining the two methods it is possible to identify the microscopic electron spin-flip mechanisms responsible for the ultrafast macroscopic magnetization dynamics of the cobalt film. In particular, we show that electron-magnon excitation does not affect the overall magnetization even though it is an efficient spin-flip channel on the sub-200 fs timescale. Instead we find experimental evidence for the relevance of Elliott-Yafet type spin-flip processes for the ultrafast demagnetization taking place on a time scale of 300 fs.

Bulk and surface states of a clean and Cs-doped surface of a Co film grown on Cu͑001͒ have been studied by spin-resolved photoemission ͑SR-PE͒ and compared with band structure calculation results. One-photon ͑1PPE͒ and two-photon ͑2PPE͒ photoemission spectra from clean Co films are found to be dominated by a peak located at a binding energy of about 0.4 eV with respect to E F , which is assigned to the spin up 3d bulk state. Slight Cs-doping of a Co͑001͒ surface shifts an image potential state in resonance with the sp-states of the conduction band. SR-2PPE study of the optically-induced electron population in such an image resonance reveals a strong dependence on the set polarization of the laser light. We are able to directly detect the spin polarization of electrons photoemitted from the image resonance state, which can be varied from highlypolarized ͑about bulk values͒ to almost unpolarized when tuning light polarization of the pump laser pulse from s to p.

In this article we investigate the surface spin polarization in a 100 nm Co 2 Cr 0.6 Fe 0.4 Al (CCFA) film grown ex situ epitaxially on MgO(100) with a 10 nm Fe buffer layer by means of spin resolved photoemission. We show that a careful in situ preparation of the sample surface leads to values for the room temperature spin polarization up to 45% at the Fermi level. To our knowledge, this is the highest value measured so far at the surface region of a full Heusler alloy at room temperature.

We have studied the possibly half metallic Co 2 F eSi full Heusler alloy by means of spin-and time-resolved photoemission spectroscopy. For excitation, the second and fourth harmonic of femtosecond Ti:sapphire lasers were used, with photon energies of 3.1 eV and 5.9 eV , respectively. We compare the dependence of the measured surface spin polarization on the particular photoemission mechanism, i.e. 1-photon-photoemission (1PPE) or 2-photon photoemission (2PPE). The observed differences in the spin polarization can be explained by a spin-dependent lifetime effect occurring in the 2-photon absorption process. The difference in escape depth of the two methods in this context suggests that the observed reduction of spin polarization (compared to the bulk) cannot be attributed just to the outermost surface layer but takes place at least 4 − 6 nm away from the surface.

We present temporal information obtained by mass spectrometry techniques about the evolution of plasmas generated by laser filamentation in air. The experimental setup used in this work allowed us to study not only the dynamics of the filament core but also of the energy reservoir that surrounds it. Furthermore, valuable insights about the chemistry of such systems like the photofragmentation and/or formation of molecules were obtained. The interpretation of the experimental results are supported by PIC (particle in cell) simulations.