Andrea Cavalleri

Abstract:

We report on the application of femtosecond x-ray scattering to experimental studies of the photo-induced, structural phase transition in VO2. The transition between the two crystalline phases of the material occurs, for sufficiently intense excitation, within 500 fs.

Abstract:

Femtosecond laser-generated plasmas emit ultrashort X-ray pulses in the multi-keV range, which allow the extension of X-ray spectroscopy into the ultrafast time-domain. We report here on the generation of such short X-ray pulses and their application for time-resolved diffraction as a means to directly study ultrafast structural dynamics in laser-excited solids.

Abstract:

Femtosecond x-ray and visible pulses were used to probe structural and electronic dynamics during an optically driven, solid-solid phase transition in VO(2). For high interband electronic excitation (approximately 5 x 10(21) cm(-3)), a subpicosecond transformation into the high-T, rutile phase of the material is observed, simultaneous with an insulator-to-metal transition. The fast time scale observed suggests that, in this regime, the structural transition may not be thermally initiated.

Abstract:

First conjunct optical and x-ray measurements were reported during an optically driven solid-solid phase transition in the correlated oxide Vo2. Optical measurements were performed by combining the pump-probe technique with visible microscopy. Laser pulses of high fluence triggered a subpicosecond structural transition from the low temperature monoclinic phase to the high temperature rutile phase.

Abstract:

Time-resolved x-ray diffraction with ultrashort ( approximately 300 fs), multi-keV x-ray pulses has been used to study the femtosecond laser-induced solid-to-liquid phase transition in a thin crystalline layer of germanium. Nonthermal melting is observed to take place within 300-500 fs. Following ultrafast melting we observe strong acoustic perturbations evolving on a picosecond time scale.