Ultrafast x-rays capture the electron and nuclear dance (Vol. 49, No. 2)

Experimental techniques used in ultrafast x-ray science

There has been revolutionary progress in producing ultrafast short-wavelength radiation and dreams of visualizing electronic and nuclear motion in complex systems on their natural timescales are rapidly unfolding. Accelerator-driven free-electron-laser sources of ultrafast, ultraintense x-ray pulses that open the door to nonlinear multiphoton x-ray phenomena, though rare (seven worldwide), have basically doubled their operating number in the past year. Laboratory-based ultrafast x-ray pulses based upon high harmonic radiation from infrared lasers, present and affordable at many institutions, have decreased in pulse duration from a longstanding record of 67 attoseconds to 43 attoseconds recently, and, have increased in photon energy to >1 keV.

The roadmap presents independent perspectives from 17 leading groups on further source developments and their potential impacts on atomic and molecular physics. We start with familiar processes, i.e. ultrafast photoexcited molecular dynamics followed with femtosecond x-ray pulses, then discuss phenomena enabled only by intense x-ray pulses from the accelerator-based free-electron-laser sources, i.e. multidimensional x-ray spectroscopies, nonlinear scattering and single-shot imaging, and conclude with the attosecond frontier where new source developments enable fundamental understanding of how charge migrates and how electrons are ejected.

L. Young and 26 co-authors, Roadmap of ultrafast x-ray atomic and molecular physics, J. Phys. B: At. Mol. Opt. Phys., 51, 032003 (2018)