Abstract
The recent progress in the development of X-ray free electron lasers (XFELs) allows for the delivery of over 1011 high-energy photons to solid-density samples in a femtosecond time scale. The corresponding peak brightness of XFEL induces a nonlinear response of matter in a short-wavelength regime. The absorption of an XFEL pulse in a solid also results in the creation of high energy density (HED) matter. The electronic structure and related fundamental properties of such HED matter can be investigated with the control of XFEL and various X-ray spectroscopic techniques. These experimental data provide unique opportunities to benchmark theories and models for extreme conditions and to guide further advances. In this article, the current progress in spectroscopic studies on intense XFEL–matter interactions and HED matter are reviewed, and future research opportunities are discussed.
Highlights
The recent progress in development of short-wavelength free-electron lasers (FELs) has opened up a variety of opportunities in diverse fields such as atomic physics, plasma physics, ultrafast chemistry, and biomolecular imaging [1,2,3,4]
High energy density (HED) science is defined as the study of matter at extreme radiation, pressure, and temperature corresponding to energy densities in excess of about 1011 J/m3 [8,9]
The development of X-ray free electron lasers (XFELs) was an important step for advancing HED science
Summary
The recent progress in development of short-wavelength free-electron lasers (FELs) has opened up a variety of opportunities in diverse fields such as atomic physics, plasma physics, ultrafast chemistry, and biomolecular imaging [1,2,3,4]. The lack of experimental techniques to quantify single-state parameters at various temperature-density conditions has posed obstacles in the measurement of the fundamental properties and testing the theoretical description of simple materials such as hydrogen, carbon, and gold in the HED states. In this context, the development of XFEL was an important step for advancing HED science. Owing to the femtosecond pulse duration, this heating absorption spectroscopies (XES/XAS) are simple but powerful diagnostics and are complimentary to each other in that they probe occupied and unoccupied electronic structures, as well as study the response to the radiations Findings from these investigations and the advances in our understanding of the HED regime will be discussed
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