Proton Acceleration with High-Intensity Ultrahigh-Contrast Laser Pulses

Abstract

We report on simultaneous measurements of backward- and forward-accelerated protons spectra when an ultrahigh intensity (approximately 5 x 10(18) W/cm(20), ultrahigh contrast (>10(10)) laser pulse interacts with foils of thickness ranging from 0.08 to 105 microm. Under such conditions, free of preplasma originating from ionization of the laser-irradiated surface, we show that the maximum proton energies are proportional to the p component of the laser electric field only and not to the ponderomotive force and that the characteristics of the proton beams originating from both target sides are almost identical. All these points have been corroborated by extensive 1D and 2D particle-in-cell simulations showing a very good agreement with the experimental data.

Energetic ions at moderate laser intensities using foam-based multi-layered targets

“…Here the change of laser intensity was achieved by means of a focal spot variation in the range 3.5 and 150 µm (FWHM), either in LC (top graph) or in HC (bottom graph) configuration. As a common feature among the different explored experimental configurations using foam-attached target, we measured proton maximum energies in excess of [6].A further remarkable aspect, compared to other examples of target structuring [3,13,14], is that the enhancement of maximum proton energy is observed independently from the laser pre-pulse intensity, i.e. both at low and high-contrast, which can constitute a simplification of the experimental setup for specific purposes.…”

Enhancement of ion generation in femtosecond ultraintense laser-foil interactions by defocusing

“…Recent studies have indicated that utilizing high contrast laser pulses to irradiate ultra-thin foils is a promising way to improve the proton beam quality and conversion efficiency. Much effort has been made to improve the contrast ratio of the laser pulses, by utilizing the ultra-fast Pockels cells, 12 plasma mirrors, [13][14][15] second harmonic generation (SHG), 16 etc.…”

Ion acceleration in electrostatic field of charged cavity created by ultra-short laser pulses of 1020–1021 W/cm2

“…More recently, similar experiments irradiating 0.015 -90 m foil targets at an intensity  10 20 W/cm 2 have also demonstrated an almost symmetric behavior for protons accelerated from rear and front target surfaces [9] with maximum proton energies of ~ 10-12 MeV. Those experiments covering the intensity range 10 18 W/cm 2 -10 20 W/cm 2 [8,9] were interpreted on the basis that the same TNSA concept of ion acceleration applied to both target surfaces. However, in Ref.…”

“…Experiments, where proton emission was measured along both rear surface and front surface target normal directions, employing ultra-high laser pulse contrast (10 10 ) at intensity 10 18 W/cm 2 , have shown almost identical proton energies for target thicknesses from 0.1 µm to 100 µm [8] with maximum proton energies up to 5 MeV. It was confirmed in these experiments that the maximum proton energies are proportional to the component of the laser electric field only and not to the ponderomotive force.…”