X-ray laser pulses snapshot the motion of Bismuth atoms in sub-picosecond resolution

The Sub-Picosecond Pulse Source (SPPS) is a prototype X-ray free electron laser built using the 2-mile-long linear accelerator at Stanford Linear Accelerator Center (SLAC), California, United States. To date, ultrafast phenomena have been mainly studied with femtosecond lasers operating at ultraviolet to infrared wavelengths; however, these wavelengths are not short enough for structural studies on atomic distances. Therefore, the emergence of short pulse laser in the hard X-ray region represents a significant challenge. Recently, at Stanford, an international collaborative team from 20 different institutions succeeded in observing the atomic motion of Bismuth crystal, which, although cubic, has a slight elongation along the diagonal called a Peierls distortion. The measurements have brought new fundamental insights into the dynamics of the material, which shows very strong coupling between the electronic and ionic structures. The results could also be used to screen many theoretical calculations made so far. For more information, see the paper, "Ultrafast Bond Softening in Bismuth: Mapping a Solid's Interatomic Potential with X-rays ", D. M. Fritz et al., Science 315, 633 (2007).