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LPA Online Seminars

Efficient laser-driven proton and bremsstrahlung generation from cluster- assembled foam targets

by Irene Prencipe (HZDR)


In this talk, we present the results of an experimental investigation of the interaction between 30 fs laser pulses and foam-coated solid foils in the relativistic regime (up to 5 × 1020 W cm−2). Aim of the study is the optimization of the laser energy conversion into laser-accelerated protons. The experiment was performed on the DRACO 150 TW laser facility at Helmholtz- Zentrum Dresden-Rossendorf. Target production and characterization were performed using techniques specially developed at Politecnico di Milano. Foam targets used in this experiment are composed of 1.5 μm-thick Al foils with ultra-low density carbon coating (thickness ~ 4-16 μm, density ~ 18 mg/cm3, corresponding to 3.2 critical densities). The effect of the foam layer on the interaction process is studied in a wide range of laser and target properties and investigated with an extended set of plasma diagnostics. Proton acceleration performances show a pronounced dependence on the irradiation and target geometry. A significant enhancement is observed in optimal conditions for foam targets in terms of proton cut-off energy (18.5 MeV) and number of protons above 4.7 MeV (4 × 109 protons/shot) with respect to uncoated foils (9.5 MeV, 1 × 109 protons/shot), together with a sixfold increase in the bremsstrahlung yield. This enhancement is attributed to increased laser absorption and electron generation in the foam meso- and nanostructure. Signatures of the laser-foam interaction were observed in electron spectra and distributions, bremsstrahlung signal, scattered light patterns and ion acceleration 45° from the target normal direction.