Research Highlights

1. Ultrafast melting of diamond:

"An international team of scientists has found evidence of an unconventional 'non-thermal' melting process in diamond induced by an intense X-ray free-electron laser beam. While in conventional melting the heated atoms of a sample start moving stronger and stronger until the interatomic bonds break, the intense X-ray laser flashes can excite so many electrons that this reorganizes the interatomic potential on femtosecond timescale and breaks the bonds between carbon atoms apart straight away. The scientists around Ichiro Inoue from the RIKEN SPring-8 Center in Japan, Eiji Nishibori from University of Tsukuba in Japan and DESY & INP PAS scientist Beata Ziaja have recently reported their observations on X-ray induced ultrafast melting of diamond in the journal Physical Review Letters (2021):"

See DESY News [], DESY Highlights 2021, DESY FEMTO 02/21, page 31,[]

2. Towards better temporal diagnostics of ultrafast X-ray pulses:

''Spatially encoded measurements of transient optical transmissivity became a standard tool for temporal diagnostics of free-electron-laser (FEL) pulses. The modern experimental techniques can measure changes in such optical coefficients with a temporal resolution better than 10 fs. This, in an ideal case, would imply a similar resolution for the temporal pulse properties and the arrival time jitter between the FEL and optical laser pulses. The observed changes of transient optical coefficients are due to the emergent carriers, electron and holes, produced in the X-ray excited material. However, additional processes such as carrier transport and carrier recombination can make the diagnostic measurement inaccurate. In a combined experimental and theoretical study, an international team, with participating IFJ PAN scientists, identified the main processes contributing to the unwanted escape of carriers during diagnostic measurement. By controlling their contribution in future applications, one can gain a very high temporal resolution for the reconstruction of FEL pulse properties measured with semiconductor based diagnostic tools. The results have been published in the journal Scientific Reports (2021): ''

See INP PAS News []

3. Versatile tool XTANT+ to study response of various materials to X-ray pulses:

''Intense X-ray pulses from free-electron lasers can trigger ultrafast electronic, structural and magnetic transitions in solid materials, within a material volume which can be precisely shaped through adjustment of X-ray beam parameters. This opens unique prospects for material processing with X-rays. However, any fundamental and applicational studies are in need of computational tools, able to predict material response to X-ray radiation. Here we present a dedicated computational approach XTANT+ developed to study X-ray induced transitions in a broad range of solid materials, including those of high chemical complexity. The latter becomes possible due to the implementation of the versatile density functional tight binding code DFTB+ to follow band structure evolution in irradiated materials. The outstanding performance of the implementation is demonstrated with a comparative study of XUV induced graphitization in diamond. The results have been published in the journal Scientific Reports (2022): https://"