Electronic temperature effects on the optical response of silver nanoparticles

The electronic temperature dependence of the optical absorption of silver nanoparticles is investigated in the framework of the time-dependent local-density approximation at finite temperature. Below the spectral region of interband transitions, we have found that the electronic temperature leads to a broadening and spectral shift of the surface plasmon resonance. The calculated differential transmission is in good agreement with recent experimental measurements obtained with time resolved pump-probe techniques

Dynamique ultra-rapide de réseaux périodiques de trous sub-longueur d'onde dans des films métalliques

Nous avons étudié, par spectroscopie femtoseconde, la transmission différentielle de réseaux périodiques de trous sub-longueur d'onde inscrits dans des films métalliques d'or. En particulier, nous avons montré que le comportement dynamique de la fonction diélectrique $\varepsilon$ du métal permet d'expliquer la dynamique spectrale des deux résonances présentes dans le spectre linéaire de nos nanostructures

Ultrafast angular momentum transfer in multisublattice ferrimagnets

Équipe 101 : Nanomagnétisme et électronique de spinInternational audienceFemtosecond laser pulses can be used to induce ultrafast changes of the magnetization in magnetic materials. However, one of the unsolved questions is that of conservation of the total angular momentum during the ultrafast demagnetization. Here we report the ultrafast transfer of angular momentum during the first hundred femtoseconds in ferrimagnetic Co0.8Gd0.2 and Co0.74Tb0.26 films. Using time-resolved X-ray magnetic circular dichroism allowed for time- resolved determination of spin and orbital momenta for each element. We report an ultrafast quenching of the magnetocrystalline anisotropy and show that at early times the demagnetization in ferrimagnetic alloys is driven by the local transfer of angular momenta between the two exchange- coupled sublattices while the total angular momentum stays constant. In Co0.74Tb0.26 we have observed a transfer of the total angular momentum to an external bath, which is delayed by similar to 150 fs

Ultrafast spin dynamics of an individual CoPt

We have studied the ultrafast magneto-optical response of CoPt3 ferromagnetic nanodots with diameters ranging from 0.2 to 1 μm. Our experiments combine an accurate temporal resolution using femtosecond laser pulses and a high spatial resolution ($\leqslant$300 nm) obtained with a reflective confocal Kerr microscope. Our experimental approach allows exploring the dynamics of the magnetization of magnetic nanostructures over a broad temporal scale ranging from 100 fs to 1 ns. We report the corresponding relaxation behavior of the electrons and the spins initially excited with a large excess energy above the Fermi level

Time-resolved x-ray magnetic circular dichroism study of ultrafast demagnetization in a CoPd ferromagnetic film excited by circularly polarized laser pulse

The magnetization dynamics of CoPd films excited by circularly polarized ultrashort laser pulses is studied by time-resolved x-ray magnetic circular dichroism. In those films the ultrafast dynamics measured at the Co-L-3 edge is strongly sensitive to the orbitalmagnetic moment L-z. The amount of angular momentum transferred by the circularly polarized ultrashort laser pulses to the ferromagnetic films is evaluated to +/- 0.1 (h) over bar /atom, which is above the detection limit of the experiment. Despite this, no polarization-dependent difference on the magnetization dynamics could be evidenced. These results are explained by ultrafast electronic relaxation mechanisms of the transferred angular momentum, faster than similar to 100 fs. This experiment sets the methodology as well as an upper time limit for determination of angular momentum relaxation processes

Laser induced ultrafast 3d and 4f spin dynamics in CoDy ferrimagnetic alloys as a function of temperature

Authors and affiliations of this article:T. Ferté1, G. Malinowski2, E. Terrier1, V. Halté1, L. Le Guyader3, K. Holldack3, M. Hehn2, C. Boeglin1 and N. Bergeard1* 1 Université de Strasbourg, CNRS, Institut de Physique et Chimie des Matériaux de Strasbourg, UMR 7504, F-67000 Strasbourg, France. 2 Institut Jean Lamour, Université de Lorraine, BP 50840, 54011 Nancy, France3 Institut für Methoden und Instrumentierung der Forschung mit Synchrotronstrahlung Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Albert-Einstein-Str. 15, 12489 Berlin, German

Ultrafast angular momentum transfer in multisublattice ferrimagnets

Femtosecond laser pulses can be used to induce ultrafast changes of the magnetization in magnetic materials. However, one of the unsolved questions is that of conservation of the total angular momentum during the ultrafast demagnetization. Here we report the ultrafast transfer of angular momentum during the first hundred femtoseconds in ferrimagnetic Co0.8Gd0.2 and Co0.74Tb0.26 films. Using time-resolved X-ray magnetic circular dichroism allowed for time- resolved determination of spin and orbital momenta for each element. We report an ultrafast quenching of the magnetocrystalline anisotropy and show that at early times the demagnetization in ferrimagnetic alloys is driven by the local transfer of angular momenta between the two exchange- coupled sublattices while the total angular momentum stays constant. In Co0.74Tb0.26 we have observed a transfer of the total angular momentum to an external bath, which is delayed by similar to 150 fs

Femtosecond Dynamics of Light Transmission Through Sub-Wavelength Hole Arrays in Metallic Films

We report on the observation of an ultrafast modification of ~30% in the enhanced transmission through sub-wavelength nanometric apertures in metallic films. It demonstrates the feasibility of nanoscaled femtosecond optical switches