C. v. Korff Schmising

Picosecond time-resolved x-ray refectivity of a laser-heated amorphous carbon film

We demonstrate thin film x-ray reflectivity measurements with picosecond time resolution. Amorphous carbon films with a thickness of 46 nm were excited with laser pulses characterized by 100 fs duration, a wavelength of 800 nm, and a fluence of 70 mJ/cm2. The laser-induced stress caused a rapid expansion of the thin film followed by a relaxation of the film thickness as heat diffused into the silicon substrate. We were able to measure changes in film thickness as small as 0.2 nm. The relaxation dynamics are consistent with a model which accounts for carrier-enhanced substrate heat diffusivity.

Time-resolved x-ray scattering from laser-molten indium antimonide.

We demonstrate a concept to study transient liquids with picosecond time-resolved x-ray scattering in a high-repetition-rate configuration. Femtosecond laser excitation of crystalline indium antimonide (InSb) induces ultrafast melting, which leads to a loss of the long-range order. The remaining local correlations of the liquid result in broad x-ray diffraction rings, which are measured as a function of delay time. After 2 ns the liquid structure factor shows close agreement with that of equilibrated liquid InSb. The measured decay of the liquid scattering intensity corresponds to the resolidification rate of 1 m/s in InSb.

Ultrafast structure and polarization dynamics in nanolayered perovskites studied by femtosecond X-ray diffraction

The polarization and lattice dynamics in a metal/ferroelectric/metal nanolayer system is studied by femtosecond x-ray diffraction. Two Bragg reflections provide information on the coupled dynamics of the two relevant phonon modes for ferroelectricity in perovskites, the tetragonal distortion and the ion displacement. Optical excitation of the metallic SrRuO3(SRO) layers generates giant stress, compressing the ferroelectric PbTr0.2Ti0.8O3(PZT) layers by up to 2%. The maximum elongation of the tetragonal mode is reached after 1.3 ps. With a slight delay the ferroelectric polarization P is reduced by up to 100 percent that is due to the anharmonic coupling of the two modes.

Ultrafast structure and polarization dynamics in nanolayered perovskites studied by femtosecond x-ray diffraction

The polarization and lattice dynamics in a metal/ferroelectric/metal nanolayer system is analyzed by femtosecond x-ray diffraction. Optically induced giant stress in the metal layers can switch off the ferroelectric polarization within 2 ps.

Probing strain propagation in nanostructured perovskites by ultrafast x-ray diffraction

Propagating strain waves in SrTiO₃ with amplitudes of Deltaa(t)/a₀ ap 10^-4 launched from a PbZr_0.2Ti_0.8O₃ film are measured by X-ray diffraction. The shape of the picosecond transients depends nonlinearly on the strain amplitude due to X-ray interference.