M. Perner

Femtosecond dynamics of stimulated emission and photoinduced absorption in a PPP-type ladder polymer

Abstract The dynamics of optical excitations in a PPP-type ladder polymer have been investigated by means of femtosecond pump-probe experiments. Stimulated emission (SE) is observed around the S 1 → S 0 transition while photoinduced absorption (PA) dominates the differential transmission at lower energies. The stimulated emission is due to singlet exciton recombination. Comparative studies of the temporal behaviour of the SE and the PA demonstrate that the SE and the PA signals originate from different species. Our results provide evidence that the PA is due to spatially separated electron-hole pairs (indirect excitons).

Homogeneous line widths of surface plasmons in gold nanoparticles measured by femtosecond pump-and-probe and near-field optical spectroscopy

We study the damping of the surface-plasmon resonance in gold nanoparticles that is caused by high-intensity optical excitation of the electron gas. Femtosecond pump-probe experiments are performed on gold nanoparticles embedded in dielectric matrices. Optical excitation of single-electron interband transitions leads to a pronounced broadening of the surface-plasmon line, which reflects the excitation-induced damping of the collective electron oscillation. The time evolution of the damping rate follows that of the electron temperature, showing that the damping rate is strongly influenced by transient variations in the electronic scattering rate. The dependence of the damping rate on the excitation energy shows evidence for fast relaxation of the optically generated d-band holes. In addition, cw transmission experiments performed with a scanning near-field optical microscope (SNOM) on single gold nanoparticles give access to the homogeneous line width of the surface plasmon.

Nonlinear Optical Interplay Between Different Surface Plasmons in Silver Nano-Ellipsoids

Using femtosecond pump-probe experiments we measure the interplay between the two, perpendicularly polarized and spectrally separate, surface plasmons of silver nano-ellipsoids. Pulsed optical excitation leads to two normal-mode vibrations of the ellipsoidal particles.

Acoustic vibrations of silver nanoparticles

Using time-resolved pump-and-probe experiments we show that the acoustic vibrations of silver nanoparticles excited by ultrashort laser pulses are triggered by two mechanisms: the lattice anharmonicity and the thermal pressure of the hot electrons.

Nano-optics with surface plasmons

Summary form only given, as follows. Near-field optical and ultrafast nonlinear optical experiments on various metal nanostructures provide important information on the dynamical properties of surface plasmons and their use in nano-optics.