RESUMO
We investigate the vibration dynamics of ellipsoidal silver nanoparticles, using time-resolved optical pump-probe spectroscopy. When excited with femtosecond laser pulses, the particles execute anisotropic shape oscillations. We show that these vibrations are triggered by the thermal expansion of the optically heated particles. The time dependence of the vibrations indicates that this expansion is caused by two mechanisms: The lattice anharmonicity and the extremely large pressure of the hot conduction electrons.
RESUMO
We imaged magnetic domains in Pt/Co/Pt multilayers using an apertureless scanning near-field optical microscope operating in reflection mode. As the magneto-optical effects are weak for this kind of structure, a polarization modulation technique with a photoelastic modulator was used to reveal the contrast between magnetic domains. In the case of a Pt/Co/Pt trilayer structure, a strong improvement in lateral resolution is observed compared with far-field magneto-optical images and good sensitivity is achieved. In the case of a Pt/[Co/Pt]Pt multilayer structure, stripe domains of 200 nm width could be resolved, in good agreement with images obtained by magnetic force microscopy on the same structure.