Efficient Laser-Driven Proton Acceleration from a Cryogenic Solid Hydrogen Target.

We report on the successful implementation and characterization of a cryogenic solid hydrogen target in experiments on high-power laser-driven proton acceleration. When irradiating a solid hydrogen filament of 10 µm diameter with 10-Terawatt laser pulses of 2.5 J energy, protons with kinetic energies in excess of 20 MeV exhibiting non-thermal features in their spectrum were observed. The protons were emitted into a large solid angle reaching a total conversion efficiency of several percent. Two-dimensional particle-in-cell simulations confirm our results indicating that the spectral modulations are caused by collisionless shocks launched from the surface of the the high-density filament into a low-density corona surrounding the target. The use of solid hydrogen targets may significantly improve the prospects of laser-accelerated proton pulses for future applications.

K-shell spectroscopy of silicon ions as diagnostic for high electric fields.

We developed a detection scheme, capable of measuring X-ray line shape of tracer ions in µm thick layers at the rear side of a target foil irradiated by ultra intense laser pulses. We performed simulations of the effect of strong electric fields on the K-shell emission of silicon and developed a spectrometer dedicated to record this emission. The combination of a cylindrically bent crystal in von Hámos geometry and a CCD camera with its single photon counting capability allows for a high dynamic range of the instrument and background free spectra. This approach will be used in future experiments to study electric fields of the order of TV/m at high density plasmas close to solid density.

Compact cryogenic source of periodic hydrogen and argon droplet beams for relativistic laser-plasma generation.

We present a cryogenic source of periodic streams of micrometer-sized hydrogen and argon droplets as ideal mass-limited target systems for fundamental intense laser-driven plasma applications. The highly compact design combined with a high temporal and spatial droplet stability makes our injector ideally suited for experiments using state-of-the-art high-power lasers in which a precise synchronization between the laser pulses and the droplets is mandatory. We show this by irradiating argon droplets with multi-terawatt pulses.