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Epitaxially grown metallic oxide transducers support the generation of ultrashort strain pulses in SrTiO${}_{3}$ (STO) with high amplitudes up to 0.5$%$. The strain amplitudes are calibrated by real-time measurements of the lattice deformation using ultrafast x-ray diffraction. We determine the speed at which the strain fronts propagate by broadband picosecond ultrasonics and conclude that, above a strain level of approx. 0.2$%$, the compressive and tensile strain components travel at considerably different sound velocities, indicating nonlinear wave behavior. Simulations based on an anharmonic linear-chain model are in excellent accord with the experimental findings and show how the spectrum of coherent phonon modes changes with time.

We measured the ultrafast optical response of metal-dielectric superlattices by broadband all-optical pump-probe spectroscopy. The observed phase of the superlattice mode depends on the probe wavelength, making assignments of the excitation mechanism difficult. Ultrafast x-ray diffraction data reveal the true oscillation phase of the lattice which changes as a function of the excitation fluence. This result is confirmed by the fluence dependence of optical transients. We set up a linear chain model of the lattice dynamics and successfully simulated the broadband optical reflection by unit-cell resolved calculation of the strain-dependent dielectric functions of the constituting materials.

We determined experimentally the complex transient optical dielectric function of a well-characterized polyelectrolyte/gold-nanoparticle composite system over a broad spectral range upon short pulse laser excitation by simultaneously measuring the time-dependent reflectance and transmittance of white light pulses with femtosecond pump-probe spectroscopy. We extracted directly the ultrafast changes in the real and imaginary parts of the effective dielectric function, epsilon(eff)(r) (omega,t)and epsilon(eff)(i) (omega,t), from the experiment. This complete experimental set of information on the time-dependent complex dielectric function challenges theories modeling the transient dielectric function of gold particles and the effective medium.

Femtosecond excitation of ${\text{SrRuO}}_{3}$ nanolayers in a ${\text{SrRuO}}_{3}/{\text{SrTiO}}_{3}$ superlattice quenches their ferromagnetism, resulting in magnetostriction. The buildup of mechanical stress is observed in real time by mapping lattice motions via ultrafast x-ray diffraction. A rise time of 500 fs is found for a wide range of excitation wavelengths. In the ferromagnetic phase, phonon-mediated $({\ensuremath{\sigma}}_{\text{ph}})$ and magnetostrictive stress $({\ensuremath{\sigma}}_{M})$ components display similar strengths but opposite signs. The amplitude of ${\ensuremath{\sigma}}_{M}$ follows the temperature dependent magnetization ${M}^{2}(T)$ whereas the strength of ${\ensuremath{\sigma}}_{\text{ph}}$ is determined by the amount of deposited energy.

Strain propagation in a perovskite heterostructure grown on a ${\mathrm{SrTiO}}_{3}$ (STO) substrate is studied by ultrafast x-ray diffraction. Femtosecond displacive phonon excitation in a ${\mathrm{PbZr}}_{0.2}{\mathrm{Ti}}_{0.8}{\mathrm{O}}_{3}∕{\mathrm{SrRuO}}_{3}$ (PZT/SRO) film launches acoustic strain waves propagating into the STO substrate. We demonstrate a two-step time evolution of diffracted x-ray intensity which originates from different interfering contributions to the (004) Bragg peak of the STO substrate. Analysis by dynamical x-ray diffraction theory gives the absolute strain $\mathrm{\ensuremath{\Delta}}a∕{a}_{0}$ in a wide range of optical pump fluences. Ultrafast transient strain as small as $\mathrm{\ensuremath{\Delta}}a∕{a}_{0}=2\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}$ is determined in this way.