Nonequilibrium warm dense matter investigated with laser-plasma-based XANES down to the femtosecond.

The use of laser-plasma-based x-ray sources is discussed, with a view to carrying out time-resolved x-ray absorption spectroscopy measurements, down to the femtosecond timescale. A review of recent experiments performed by our team is presented. They concern the study of the nonequilibrium transition of metals from solid to the warm dense regime, which imposes specific constraints (the sample being destroyed after each shot).

Dynamics of femtosecond heated warm dense copper with time-resolved L3-edge XANES.

Combining experimental set up and molecular dynamics simulations, we were able to follow the time evolution of the X-ray absorption near edge spectrum (XANES) of a dense copper plasma. This provides a deep insight into femtosecond laser interaction with a metallic copper target. This paper presents a review of the experimental developments we made to reduce the X-ray probe duration, from approximately 10 ps to fs duration with table-top laser systems.

Femtosecond Resolution of the Nonballistic Electron Energy Transport in Warm Dense Copper.

The ultrafast electron energy transport is investigated in laser-heated warm dense copper in a high flux regime (2.5±0.7×10^{13}  W/cm^{2} absorbed).

Ultrafast Thermal Melting in Nonequilibrium Warm Dense Copper.

The ultrafast dynamics of the loss of crystalline periodicity is investigated in femtosecond laser heated warm dense copper, by the original use of x-ray absorption near-edge specific structures just above the L3 edge. The characteristic time is observed near 1 ps, for specific energy density ranging from 1 to 5  MJ/kg, using ps-resolution x-ray absorption spectroscopy. The overall experimental data are well reproduced with two-temperature hydrodynamic simulations, supporting a thermal phase transition.

Two-channel high-resolution quasi-monochromatic X-ray imager for Al and Ti plasma.

High-resolution, high-sensitivity X-ray imaging is a real challenge in high-energy density plasma experiments. We present an improved design of the Fresnel ultra high-resolution imager instrument. Using an Ultra-High-Intensity (UHI) laser to generate hot and dense plasma in a small volume of an Al-Ti mixed target provides simultaneous imaging of both Al and Ti X-ray emission.