The ultrahigh laser intensities enabled by high power lasers facilitate the generation of high energy ions using accelerating gradients many million times that of conventional accelerators. The maturation of these sources relies on breakthroughs in the generated beam parameters and improved reproducibility and repetition rate. We used two independent state-of-the-art femtosecond laser systems capable of repetitive operation to accelerate protons and carbons to high energies (>50 MeV and 30 MeV/nucleon respectively) in the relativistically induced transparency (RIT) regime. We demonstrate that acceleration is optimised for different laser prepulse levels by varying the initial target thickness, relaxing laser requirements for energetic ion generation. We elucidated the acceleration dynamics with cutting-edge 3D simulation, showing a) the role of the laser prepulse in pre-expanding the target, and b) radiation pressure assisted electron expulsion from the target during relativistically induced transparency, generating a strong space charge field which rapidly accelerates ions. Our demonstration of a robust acceleration mechanism that does not require complicated targetry nor a single-shot prepulse suppressing plasma mirror is an important step forward for developing high repetition rate applications of laser driven ion sources.
We report on the time-resolved observation of transient laser-induced breakdown (LIB) during the leading edge of high-intensity petawatt-class laser pulses with peak intensities up to 6x10^21 W/cm^2 in interaction with dielectric cryogenic hydrogen jet targets. The results show that LIB occurs much earlier than what is typically expected following the concept of barrier suppression ionization and that the laser pulse duration dependence of LIB and laser-induced damage threshold (LIDT) is very relevant to high-intensity laser-solid interactions. We demonstrate an effective approach to determine the onset of LIB, i.e. the starting point of target pre-expansion, by comparing a laser contrast measurement with a characterization study of the target specific LIB thresholds.
In this contribution, we present the results of laser-target interaction studies with intensities ranging from the relativistic regime down to the intensities of dielectric breakdown of hydrogen. They were conducted using the cryogenic hydrogen jet platforms together with the high-resolution optical probing capabilities at the Draco laser facility at Helmholtz-Zentrum Dresden-Rossendorf and the HiBEF facility at European XFEL. Changing the laser parameters enables to utilize specific plasma processes for controlled plasma density tailoring. These results, together with technical advancements of the target, pave the way towards a stable platform for near-critical density targets that will enable stable, repetition-rated proton sources for a multitude of applications at superb energies.
Compact tuneable sources of ultrashort hard x-ray pulses can be realized by Thomson scattering, taking advantage
of the comparatively short wavelength of a scattered laser pulse with respect to the period length of
conventional undulators. Here, we present a detailed analysis and optimization of the efficiency of linear and
non-linear Thomson scattering when the process is driven with relativistic laser pulses and when the conventional
accelerator is replaced by a laser-plasma wakefield accelerator.
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