The creation of large-volume, gradient-free warm dense matter with an x-ray free-electron laser

Abstract

International audienceThe efficiency and uniformity of heating induced by hard x-ray free-electron laser pulse is investigated for 0.5 mu m silver foils using the X-ray Pump Probe instrument at the Linac Coherent Light Source facility. Intense 8.9 keV x-ray pulses of 60 fs duration deposit energy predominantly via inner-shell ionization to create a non-equilibrium Ag solid density plasma. The x-ray pulses are focused to 14 X 17 mu m(2) by means of beryllium lenses and by varying the total beam energy, the energy deposition is varied over a range of irradiances from 4.4 to 6.5 X 10(15) W/cm(2). Two time-and-space resolved interferometers simultaneously probed the expansion of the front and rear sample surfaces and find evidence of a nearly symmetric expansion pointing to the uniformity of energy deposition over the full target thickness. The experimental results are compared with two different hydrodynamic simulations of the sample expansion. The agreement between experimental and theoretical results yields an estimate of the temperature evolution as a function of x-ray irradiance that varies from 8 to 10 eV for the x-ray irradiances studied. (C) 2015 AIP Publishing LLC

Molecular-dynamics approach for studying the nonequilibrium behavior of x-ray-heated solid-density matter

“…Delivering high x-ray fluence can increase the probabilities of photoionization processes to saturation [3]. Nonlinear phenomena arise because of the complex multiphoton ionization pathways within molecular or dense plasma environment [4][5][6][7][8]. Theory has a key role in revealing the importance of different mechanisms in the dynamics.…”

Uniform heating of materials into the warm dense matter regime with laser-driven quasimonoenergetic ion beams

“…Rapid heating of matter using a short (ps to tens of fs) laser pulse is an emerging research area in plasma physics [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18]. In these settings, the interaction between intense light and matter is sufficiently strong and fast for the atoms to be ionized instantaneously and the resulting electrons or ions (or both) attain large kinetic energies very quickly.…”

“…A recent study by Lévy et al [14] showed that uniform heating can be achieved for a 0.5 m thick silver target using a free electron x-ray laser beam, but a uniform heating of a thicker target (>1 m) has yet to be reported using this approach.…”

Measurement of the equation of state of solid-density copper heated with laser-accelerated protons

“…Recent advances have enabled access to WDM states far from the principal shock Hugoniot through the rapid, isochoric heating of a solid density sample. This is achieved using heating drivers such as hot electrons from direct intense pulsed laser irradiation of a sample [6][7][8], ultra-bright x-rays from next generation light sources [9,10], and MeV pulsed ions. Ion pulses sufficient for heating to WDM temperatures can be achieved at accelerator facilities [11], or by pulsed laser acceleration [12,13], with the later delivering ions in a much shorter pulse (picoseconds vs nanoseconds), rapidly heating targets of several micron thickness volumetrically to several eV temperatures over an area of > 100 µm.…”