Optimization of laser-nanowire target interaction to increase the proton acceleration efficiency

Abstract

We report on improved proton acceleration from the interaction of a short pulse high intensity laser (>10 20 Wcm −2 ) with nano-engineered targets. Planar targets (from 7 to 20 μm) with protruding gold nanowires having different total areal densities, lengths, and diameters, ranging from 3% to 60% of the size of the laser focal spot were used during an experimental campaign at the 3 J, 30 fs HERCULES laser facility. The results show the importance of the average number of nanowires per focal spot, N, on laser energy absorption. We show that the proton acceleration is significantly improved by using 1 nanowires per focal spot. Detailed analysis indicates that 1 nanowire per focal spot optimizes the interaction between laser pulse and nanowires, in which the wings of the pulse pull out electrons from the wires forming a plasma with density that allows for deep penetration of the laser pulse into the array. When moving away from this optimum in both directions, N=1 and N?1, the laser pulse-nanowire coupling is either too weak or unfavorable for obtaining maximum proton energy. Proton spectra are compared to simulations using 2D-3V particle-in-cell code which reproduces the experimental data with good agreement.

Enhanced laser-driven proton acceleration using nanowire targets

“…They show a measured hot electron temperature increase by a factor of 2 at lower laser intensity. Secondly, Dozières et al 51 used NW targets and obtained a maximum energy enhancement factor in the range 1.5–2. In the same work, an experimental evaluation of the influence of d and g was performed, recommending a thorough evaluation of influence of length l in a subsequent study.…”

“…The effect of the NW’s geometrical parameters are related to theoretical models for plasma expansion in vacuum 52 . The experimental study is complementary to Dozières et al 51 and focuses on the NW length l as the main investigated parameter. Using experimental NW targets, we find average proton enhancement ratios of 2 and 3 for maximum energy and temperature respectively, as well as multiple-fold proton number enhancement.…”

Generation mechanism of 100 MG magnetic fields in the interaction of ultra-intense laser pulse with nanostructured target

“…The interaction of relativistically intense laser pulses with solid targets has stimulated considerable interest because of its practical applications in laser-driven particle acceleration [1][2][3][4][5][6][7] , high-brightness ultrafast hard X-ray and K α source [8][9][10][11] , cancer treatment [12,13] , fast ignition in inertial confinement fusion [14] , etc. A crucial issue, in all these applications, is to produce high-quality forward hot electrons efficiently.…”

Copious positron production by femto-second laser via absorption enhancement in a microstructured surface target

“…1. A MST is a solid planar target with fabricated fine structures, such as layers 22 , wires [23][24][25][26][27][28] , slots 29 or holes 30 on its surface. By the surface modulation, the interaction between laser and target can be changed from "surface heating" to "volume heating", thus increasing laser absorption and electron heating 25 .…”

“…By the surface modulation, the interaction between laser and target can be changed from "surface heating" to "volume heating", thus increasing laser absorption and electron heating 25 . MSTs have been widely used in the Kα-rays production 23,24 , electron acceleration 22,25,26,30 , ion acceleration 27,29 and neutron generation 28 . Here, we firstly propose to use a MST to enhance positron production.…”