Towards the use of XFEL facilities for creation of warm dense matter and phase transition probing

by Anna Lévy (UPMC)

Friday 6 Mar 2015, 11:00 → 12:00 Europe/Berlin

AER19/4.14 (European XFEL GmbH)

The development of XFEL facilities opens important progresses in different fields thanks to their remarkable properties in terms of pulse duration, high brilliance and photon energy. Illustrating these capabilities, two main topics will be addressed related to an experiment performed at the LCLS facility and to an ongoing project that we are developing. The first part of this talk aims to demonstrate the possibility of creating large-volume, gradient-free warm dense sample with an x-ray free-electron laser and, in the case of this experiment at the hard x-ray beamline (X-ray Pump Probe-XPP) of the LCLS instrument. This warm dense matter regime, which is barely described by present-day theoretical models, is poorly understood due to the difficulty of achieving these conditions in a manner that allows accurate diagnosis. The development of free electron lasers opens a unique opportunity to generate this regime in laboratory allowing one to efficiently and uniformly heat the matter up to 10 eV within less than 100 fs. In this context, we irradiated thin Ag foils with a 9 keV x-ray beam of 60 fs duration and an intensity approaching 1016 W/cm2, monitoring the sample temperature and heating uniformity in theses experimental conditions. The results obtained led us to develop a specific code describing the x-ray energy deposition and sample relaxation which shed light on the mechanisms occurring in this regime of interaction. The second part is dedicated to the recent project developed in our laboratory aiming to probe ultrafast solid-liquid phase transition in metallic nanoparticle beams induced by femtosecond lasers. The scientific objective aims to explore the relaxation dynamic at the sub-picosecond timescale by a time-resolved measurement of the valence band sample modification after the laser pulse energy deposition. The different technical challenges inherent to this project will be presented as well as the status of preliminary experiments. This study is devoted to be performed on XFEL facilities and, within this perspective, the technical requirements for the corresponding x-ray beamline will be discussed.