Abstract
An efficient way to enhance laser-driven proton acceleration is by increasing the laser-to-target energy transfer, which can be obtained using nanostructured target surfaces. In this paper, we show that inexpensive and easily producible solid target nanostructuration using ultrasmall nanoparticles having 10 nm in diameter exhibits a nearly twofold maximum proton energy and proton number enhancement. Results are confirmed by particle-in-cell simulations, for several laser pulse lengths. A parameter scan analyzing the effect of the nanoparticle diameter and space gap between the nanospheres shows that the gap has a stronger influence on the enhancement mechanism than the sphere diameter.
Highlights
Laser-driven proton acceleration, as obtained by the interaction of a high-intensity laser with a target, is a growing field of interest, in particular, for the different potential applications that are consolidating or emerging
The most common proton acceleration mechanisms that is obtained on typical commercially available multihundred terawatt laser systems is the so-called target-normal sheath acceleration (TNSA) [17], in which protons are accelerated at the rear target surface of a solid foil, typically made of Au, Ag, Al, or CH, that is irradiated by a high-intensity (I > 1018 W=cm2), short pulse (t < 1 ps) laser operating at wavelengths around 800–1056 nm
The laser-to-target absorption, i.e., how much energy is transferred from the laser to the target and from there to the particles, is a crucial parameter, since it allows improving the efficiency of the acceleration mechanism
Summary
The laser parameters were, respectively, for the TITAN laser an energy E ∼ 220 J, pulse duration τ 1⁄4 700 fs, and central wavelength λ0 1⁄4 1.054 μm and for the ELFIE laser an energy E ∼ 12 J, pulse duration τ 1⁄4 350 fs, and central wavelength λ0 1⁄4 1.057 μm Both lasers were focused down by an f=3 off-axis parabola to about 8–10 μm focal spot diameter (FWHM), yielding an intensity I ∼ 3 × 1019 − 5 × 1020 W=cm on target. We considered this target material since it is one of the most used and cheapest target materials in laserdriven proton acceleration, was producing the best results compared to other materials and thicknesses when used as a proton source [13,39], and the wetting properties between (a)
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