Laser-driven low energy electron beams for single-shot ultra-fast probing of meso-scale materials and warm dense matter.

Laser wakefield acceleration has proven to be an excellent source of electrons and X-rays suitable for ultra-fast probing of matter. These novel beams have demonstrated unprecedented spatial and temporal resolution allowing for new discoveries in material science and plasma physics. In particular, the study of dynamic processes such as non-thermal melt and lattice changes on femtosecond time-scales have paved a way to completely new scientific horizons. Here, we demonstrate the first single-shot electron radiography measurement using an femtosecond electron source based on the downramp-density gradient laser-wakefield-acceleration with the use of a compact Ti:sapphire laser. A quasi-monoenergetic electron beam with mean energy of 1.9 ± 0.4 MeV and charge 77 ± 47 pC per shot was generated by the laser incident onto a gas target and collimated using a two ring-magnet beam path. High quality electron radiography of solid objects with spatial resolution better than 150 [Formula: see text]m was demonstrated. Further developments of this scheme have the potential to obtain single-shot ultrafast electron diffraction from dynamic lattices. This scheme poses a great promise for smaller scale university laboratories and facilities for efficient single-shot probing of warm dense matter, medical imaging and the study of dynamic processes in matter with broad application to inertial confinement fusion and meso-scale materials (mg g/cm[Formula: see text]).

Laser-plasmas in the relativistic-transparency regime: Science and applications.

Laser-plasma interactions in the novel regime of relativistically induced transparency (RIT) have been harnessed to generate intense ion beams efficiently with average energies exceeding 10 MeV/nucleon (>100 MeV for protons) at "table-top" scales in experiments at the LANL Trident Laser. By further optimization of the laser and target, the RIT regime has been extended into a self-organized plasma mode. This mode yields an ion beam with much narrower energy spread while maintaining high ion energy and conversion efficiency. This mode involves self-generation of persistent high magnetic fields (∼104 T, according to particle-in-cell simulations of the experiments) at the rear-side of the plasma. These magnetic fields trap the laser-heated multi-MeV electrons, which generate a high localized electrostatic field (∼0.1 T V/m). After the laser exits the plasma, this electric field acts on a highly structured ion-beam distribution in phase space to reduce the energy spread, thus separating acceleration and energy-spread reduction. Thus, ion beams with narrow energy peaks at up to 18 MeV/nucleon are generated reproducibly with high efficiency (≈5%). The experimental demonstration has been done with 0.12 PW, high-contrast, 0.6 ps Gaussian 1.053 µm laser pulses irradiating planar foils up to 250 nm thick at 2-8 × 1020 W/cm2. These ion beams with co-propagating electrons have been used on Trident for uniform volumetric isochoric heating to generate and study warm-dense matter at high densities. These beam plasmas have been directed also at a thick Ta disk to generate a directed, intense point-like Bremsstrahlung source of photons peaked at ∼2 MeV and used it for point projection radiography of thick high density objects. In addition, prior work on the intense neutron beam driven by an intense deuterium beam generated in the RIT regime has been extended. Neutron spectral control by means of a flexible converter-disk design has been demonstrated, and the neutron beam has been used for point-projection imaging of thick objects. The plans and prospects for further improvements and applications are also discussed.