Pushing atoms on a swing

The typical time scale of atomic motion during fundamental physical processes such as phase transitions in solids or molecular dynamics in chemical reactions ranges from ten to hundreds of femtoseconds. The direct observation of these processes on an atomic length scale therefore requires utrashort light pulses at wavelengths capable of resolving the underlying atomic structures. For these reason significant efforts have been undertaken in the past decades to develop femtosecond sources operating in the hard x-ray spectral domain. At the Swiss Light Source we have recently commissioned an undulator source offering spatially and temporally stable x-ray pulses of ~100 fs duration that are tunable in the angstrom range. The temporal characteristics of the x-ray pulses are determined studying high-amplitude phonon dynamics of photo-excited bismuth. Optical control of real space atomic motion is successfully demonstrated.

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