The interaction of intense ultrashort laser pulses with cryogenic He planar jets

Abstract

We study the interaction of intense ultrashort laser pulses with cryogenic He jets using 2d/3v relativistic Particle-in-Cell simulations (XOOPIC). Of particular interest are laser intensities (10 15 − 10 20 ) W/cm 2 , pulse lengths ≤ 100 fs, and the frequency regime ∼ 800 nm for which the jets are initially transparent and subsequently not homogeneously ionized. Pulses ≥ 10 16 W/cm 2 are found to drive ionization along the jet and outside the laser spot, the ionization-front propagates along the jet at a fraction of the speed of light. Within the ionized region, there is a highly transient field, which may be interpreted as two-surface wave decay and as a result of the chargeneutralizing disturbance at the jet-vacuum interface. The ionized region has solid-like densities and temperatures of few to hundreds of eV, i.e., warm and hot dense matter regimes. Such extreme conditions are relevant for high-energy densities as found, e.g., in shock-wave experiments and inertial confinement fusion studies. The temporal evolution of the ionization is studied considering theoretically a pump-probe x-ray Thomson scattering (XRTS) scheme. We observe plasmon and non-collective modes that are generated in the jet, and their amplitude is proportional to the ionized volume.Our theoretical findings could be tested at free-electron laser facilities such as FLASH and the European XFEL (Hamburg) and the LCLS (Stanford).Keywords: Warm and hot dense matter, pump-probe x-ray Thomson scattering experiments, dense plasma jets, two surface plasmon decay.

A sensitive EUV Schwarzschild microscope for plasma studies with sub-micrometer resolution

“…Accordingly, EUV radiation can propagate into the plasma volume, in contrast to optical radiation in the visible or near-infrared spectrum which launches density waves. 19 With an absorption length of 9 µm for the 13.5 nm EUV radiation in our experiments, the EUV pulses are sufficiently absorbed and isochorically heat the cryogenic hydrogen target by photo ionization. We have recently shown that microscopic plasma properties can be investigated by EUV scattering: the elastic scattering cross section increases by more than a factor of two when solid density hydrogen dissociates and becomes ionized as a result of electron-ion heat transfer.…”

Ionization dynamics of dense matter generated by intense ultrashort X‐ray pulses

“…The density and temperature profiles throughout the target are usually inhomogeneous. The resulting compression factor, degree of ionization, and temperature are dependent on the intensity and length of the laser pulse, its shape, and spot size . XRTS is then used to probe the WHDM state.…”