We review recent experiments on the fast and ultrafast all-optical control of light in bulk nematic and smectic-A liquid
crystals. Ultrafast optical control at sub-picosecond time scalecan be achieved via the optical Kerr response of a nematic
liquid crystal. We show that the refractive index changes are of the order of 10-4 in 5CB nematic liquid crystal and can be
optically induced by applying 100 fs pulses of 4 mJ/cm2 fluence. We discuss stimulated emission depletion of
fluorescence in a smectic-A liquid crystal and demonstrate nanosecond light control of fluorescent pulse shaping. Both
methods could be applied to control light by light in future photonic devices based on liquid crystals.
We investigate the light-induced magnetization reversal in samples of rare-earth transition metal alloys, where we aim to
spatially confine the switched region at the nanoscale, with the help of nano-holes in an Al-mask covering the sample.
First of all, an optimum multilayer structure is designed for the optimum absorption of the incident light. Next, using
finite difference time domain simulations we investigate light penetration through nano-holes of different diameter. We
find that the holes of 200 nm diameter combine an optimum transmittance with a localization better than λ/4. Further,
we have manufactured samples with the help of focused ion beam milling of Al-capped TbCoFe layers. Finally,
employing magnetization-sensitive X-ray holography techniques, we have investigated the magnetization reversal with
extremely high resolution. The results show severe processing effects on the switching characteristics of the magnetic
Skyrmions, which have originally been introduced to explain how baryons could topologically emerge from a continuous meson field, have found many exciting applications in condensed-matter physics, where they describe topological states of matter in a wide range of systems. In magnetic materials they emerge as excitations corresponding to a spin arrangement in which the spins point in all the directions wrapping a sphere. Skyrmions have indeed been observed in chiral magnets, where they form regular lattices and are stabilized under an external magnetic field thanks to the presence of the Dzyaloshinskii-Moriya interaction (DMI). More recently, a new mechanism of Skyrmion materialization has been proposed, in which the frustration introduced in a thin ferromagnetic film by the magnetic dipole-dipole interaction leads to the stabilization of Skyrmions larger than those stabilized by DMI, consisting of magnetic domains at the center of which the magnetization points out of the film plane in the opposite direction with respect to the magnetization of the surrounding material. We report about the real-space observation by means of near-field optical Faraday microscopy of such stable Skyrmions in a thin TbFeCo film. The Skyrmions are generated after local excitation of the magnetic system by means of an intense laser pulse and do not need an external magnetic field for stabilization. The unique combination of ultrashort laser-induced magnetic excitation with subdiffraction near-field optical microscopy allows us not only to produce and observe Skyrmions as individual entities, but to also create and characterize bound Skyrmion-antiSkyrmion pairs, forming a topologically neutral entity.