@article{12152,
  author = {Linda Young and Kiyoshi Ueda and Markus Gühr and Philip Bucksbaum and Marc Simon and Shaul Mukamel and Nina Rohringer and Kevin Prince and Claudio Masciovecchio and Michael Meyer and Artem Rudenko and Daniel Rolles and Christoph Bostedt and Matthias Fuchs and David Reis and Robin Santra and Henry Kapteyn and Margaret Murnane and Heide Ibrahim and François Légaré and Marc Vrakking and Marcus Isinger and David Kroon and Mathieu Gisselbrecht and Anne Huillier and Hans Wörner and Stephen Leone},
  title = {Roadmap of ultrafast x-ray atomic and molecular physics},
  abstract = {X-ray free-electron lasers (XFELs) and table-top sources of x-rays based upon high harmonic generation (HHG) have revolutionized the field of ultrafast x-ray atomic and molecular physics, largely due to an explosive growth in capabilities in the past decade. XFELs now provide unprecedented intensity (1020 W cm−2) of x-rays at wavelengths down to ∼1 � ngstrom, and HHG provides unprecedented time resolution (∼50 attoseconds) and a correspondingly large coherent bandwidth at longer wavelengths. For context, timescales can be referenced to the Bohr orbital period in hydrogen atom of 150 attoseconds and the hydrogen-molecule vibrational period of 8 femtoseconds; wavelength scales can be referenced to the chemically significant carbon K-edge at a photon energy of ∼280 eV (44 � ngstroms) and the bond length in methane of ∼1 � ngstrom. With these modern x-ray sources one now has the ability to focus on individual atoms, even when embedded in a complex molecule, and view electronic and nuclear motion on their intrinsic scales (attoseconds and � ngstroms). These sources have enabled coherent diffractive imaging, where one can image non-crystalline objects in three dimensions on ultrafast timescales, potentially with atomic resolution. The unprecedented intensity available with XFELs has opened new fields of multiphoton and nonlinear x-ray physics where behavior of matter under extreme conditions can be explored. The unprecedented time resolution and pulse synchronization provided by HHG sources has kindled fundamental investigations of time delays in photoionization, charge migration in molecules, and dynamics near conical intersections that are foundational to AMO physics and chemistry. This roadmap coincides with the year when three new XFEL facilities, operating at � ngstrom wavelengths, opened for users (European XFEL, Swiss-FEL and PAL-FEL in Korea) almost doubling the present worldwide number of XFELs, and documents the remarkable progress in HHG capabilities since its discovery roughly 30 years ago, showcasing experiments in AMO physics and other applications. Here we capture the perspectives of 17 leading groups and organize the contributions into four categories: ultrafast molecular dynamics, multidimensional x-ray spectroscopies; high-intensity x-ray phenomena; attosecond x-ray science.},
  year = {2018},
  journal = {Journal of Physics B: Atomic, Molecular and Optical Physics},
  volume = {51},
  number = {3},
  pages = {032003},
  month = {2020-01},
  publisher = {IOP Publishing},
  url = {https://doi.org/10.1088%2F1361-6455%2Faa9735},
  doi = {10.1088/1361-6455/aa9735},
}