Abstract
Laser-plasma proton acceleration was investigated in the target normal sheath acceleration regime with a target composed of a gas layer and a thin foil. The laser’s shape, duration, energy and frequency are modified as it propagates in the gas, altering the laser-solid interaction leading to proton acceleration. The modified properties of the laser were assessed by both numerical simulations and by measurements. The 3D particle-in-cell simulations have shown that a nearly seven-fold increase in peak intensity at the foil plane is possible. In the experiment, maximum proton energies showed high dependence on the energy transmission of the laser through the gas and a lesser dependence on the size and shape of the pulse. At high gas densities, where high intensity was expected, laser energy depletion and pulse distortion suppressed proton energies. At low densities, with the laser focused far behind the foil, self-focusing was observed and the gas showed a positive effect on proton energies. The promising results of this first exploration motivate further study of the target.
Highlights
Laser-plasma ion acceleration is commonly accomplished using a thin ∼ 1 μm foil as a target
Laser-plasma proton acceleration was investigated in the Target Normal Sheath Acceleration (TNSA) regime using a novel gas-foil target
For a given laser pulse and gas density profile, pulse propagation is determined by the density of the gas ne0 and the vacuum focal plane of the laser zfoc
Summary
Laser-plasma ion acceleration is commonly accomplished using a thin ∼ 1 μm foil as a target. Within the TNSA regime, many different targets have been theorized and demonstrated, aiming for improving ion beam parameters over the simple thin foil target These include coating the foil with foams [2,3,4,5,6], nanospheres [7], micropillar arrays [8], microchannels [9] and even bacteria [10]. In another approach, the foil is pre-irradiated by a weaker pulse, creating a plasma density gradient which can be controlled by the delay between the main and pre-pulse [11,12,13,14,15,16,17,18,19,20]. These methods exhibit improved performance mainly due to enhanced laser absorption in the first near-critical density layer which eventually translates into higher ion energies
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