Andrea Cavalleri

Abstract:

Optical-pump terahertz-probe spectroscopy is used to investigate the photoinduced insulator-to-metal phase transition in vanadium dioxide. The observed dynamics are consistent with a spatially inhomogeneous insulating state. © 2005 Optical Society of America.

Abstract:

In condensed matter, light propagation near resonances is described in terms of polaritons, electro-mechanical excitations in which the time-dependent electric field is coupled to the oscillation of charged masses. This description underpins our understanding of the macroscopic optical properties of solids, liquids and plasmas, as well as of their dispersion with frequency. In ferroelectric materials, terahertz radiation propagates by driving infrared-active lattice vibrations, resulting in phonon-polariton waves. Electro-optic sampling with femtosecond optical pulses can measure the time-dependent electrical polarization, providing a phase-sensitive analogue to optical Raman scattering. Here we use femtosecond time-resolved X-ray diffraction, a phase-sensitive analogue to inelastic X-ray scattering, to measure the corresponding displacements of ions in ferroelectric lithium tantalate, LiTaO(3). Amplitude and phase of all degrees of freedom in a light field are thus directly measured in the time domain. Notably, extension of other X-ray techniques to the femtosecond timescale (for example, magnetic or anomalous scattering) would allow for studies in complex systems, where electric fields couple to multiple degrees of freedom.

Abstract:

Optical-pump terahertz-probe spectroscopy is used to investigate the photoinduced insulator-to-metal phase transition in vanadium dioxide. The observed dynamics are consistent with a spatially inhomogeneous insulating state. © 2005 Optical Society of America.

Abstract:

We review our work on the photo-induced insulator-metal transition in the strongly-correlated, spin-Peierls compound VO2. Our pump-probe experiments exploit the full spectral range of modern femtosecond science, combining time-resolved mid-IR and visible techniques with ultrafast soft x-ray absorption and hard x-ray diffraction. We also report on the switching behavior of VO2 nanoparticles embedded in Silica or in optical fibers, a new route to incorporate complex, photo-active materials into technologically viable environments. ©2006 The Physical Society of Japan.

Abstract:

We photoexited a charge-ordered organic salt (EDO-TTF)2PF6 with sub-10-fs optical pulses. The photo-induced metallic phase appeared within 50-fs after pumping, characterized by large changes in reflectivity (ΔR/R~0.8) followed by strong coherent phonon modulation. © 2006 Optical Society of America.