Abstract
A high-energy, high-yield proton beam with a good homogeneous profile has been generated from a nanosphere target irradiated by a short (30-fs), intense ($7\ifmmode\times\else\texttimes\fi{}{10}^{20}\text{ }\text{ }\mathrm{W}/{\mathrm{cm}}^{2}$) laser pulse. A maximum proton energy of 30 MeV has been observed with a high proton number of $7\ifmmode\times\else\texttimes\fi{}{10}^{10}$ in the energy range 5--30 MeV. A homogeneous spatial profile with a uniformity (standard deviation from an average value within 85% beam area) of 15% is observed with the nanosphere dielectric target. Particle-in-cell simulations show the enhancement of proton cutoff energy and proton number with the nanosphere target and reveal that the homogeneous beam profile is related with a broadened angular distribution of hot electrons, which is initiated by the nanosphere structure. The homogeneous spatial properties obtained with the nanosphere target will be advantageous in developing laser-driven proton sources for practical applications in which high-quality beams are required.
Highlights
In the past decade, great attention has been paid to laser-driven ion acceleration as an innovative approach for medical applications, especially cancer therapy [1]
Particle-in-cell simulations show the enhancement of proton cutoff energy and proton number with the nanosphere target and reveal that the homogeneous beam profile is related with a broadened angular distribution of hot electrons, which is initiated by the nanosphere structure
The main motivation of our work is to extend the validity of such an acceleration mechanism at higher laser intensities and to report the improved homogeneity of the proton beam spatial profile in order to show its potential use when higher proton energies (100-MeV level), which are needed for medical applications, are obtained
Summary
Great attention has been paid to laser-driven ion acceleration as an innovative approach for medical applications, especially cancer therapy [1]. Despite the fast progress and great potential of laser-driven ion acceleration, a number of issues including the increase of proton energy up to a few hundreds of MeV, high-conversion efficiency, reduced shot-to-shot. As an effort in this direction, a micron-thick plastic foil target covered by a nanosphere monolayer was proposed [13], and its capability of producing ∼10-MeV proton beams with enhanced conversion efficiency was experimentally demonstrated by using a 100-TW-class laser at an intensity of 5 × 1019 W=cm2 [14]. The main motivation of our work is to extend the validity of such an acceleration mechanism at higher laser intensities and to report the improved homogeneity of the proton beam spatial profile in order to show its potential use when higher proton energies (100-MeV level), which are needed for medical applications (namely, hadron therapy), are obtained
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