Description
Proton beams generated via Target Normal Sheath Acceleration1,2 (TNSA) using the VEGA PW-class laser at CLPU were studied by covering pulse durations from 30–500 fs at fixed laser energies, spanning intensities from 2 × 1018 to 2 × 1020 W/cm2. This provided a unique, consistent dataset from a single campaign. Results show cut-off proton energies distribution versus pulse duration exhibit a maximum that scales with laser energy, occurring at intensities within 1 × 1019 and 2 × 1019 W/cm2, thus revealing a saturation mechanism in proton acceleration which differ with several published scaling from picosecond-driven experiments. Data analysis, supported by theoretical models and simulations, indicates this behaviour is linked to VEGA high contrast driving ultrashort scale-length plasma expansion. Consequently, pulse duration strongly impacts efficiency, decreasing sharply for shorter pulses. Updated electrostatic model, Bayesian analysis rand numerical simulations reproduce the trend, yielding a new scaling law that identifies optimal pulse duration for given laser energies. These results3 enable improved optimization of proton beams from ultrashort femtosecond high-power lasers, with potential applications in compact ion and neutron sources, inertial confinement fusion, radioisotope production and medical physics.
[1] M. Passoni and M. Lontano, Physical Review Letters 101(11), 115001 (2010).
[2] S.C. Wilks et al., Physics of Plasmas 8, 542–549 (2001)
[3] Jose. A. Pérez-Hernández et al., Proton acceleration efficiency via ultra-short PW-class lasers, under review.
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