Accelerating Protons to Therapeutic Energies with Ultra-Intense Ultra-Clean and Ultra-Short Laser Pulses

TL;DR

This paper demonstrates that ultra-intense, ultra-clean, ultra-short laser pulses can efficiently accelerate protons to energies suitable for therapy, using simulations of laser-foil interactions at intensities up to 10^22 W/cm^2.

Contribution

The study shows the feasibility of proton acceleration to therapeutic energies using high-contrast laser pulses and optimized foil thickness, supported by detailed PIC simulations.

Findings

Proton energies up to 100-220 MeV are achievable with 150-500 TW lasers.

Optimized foil thickness enhances proton acceleration efficiency.

Peaked high-energy proton spectra are suitable for radiation therapy.

Abstract

Proton acceleration by high-intensity laser pulses from ultra-thin foils for hadron therapy is discussed. With the improvement of the laser intensity contrast ratio to 10-11 achieved on Hercules laser at the University of Michigan, it became possible to attain laser-solid interactions at intensities up to 1022 W/cm2 that allows an efficient regime of laser-driven ion acceleration from submicron foils. Particle-In-Cell (PIC) computer simulations of proton acceleration in the Directed Coulomb explosion regime from ultra-thin double-layer (heavy ions / light ions) foils of different thicknesses were performed under the anticipated experimental conditions for Hercules laser with pulse energies from 3 to 15 J, pulse duration of 30 fs at full width half maximum (FWHM), focused to a spot size of 0.8 microns (FWHM). In this regime heavy ions expand predominantly in the direction of laser pulse propagation enhancing the longitudinal charge separation electric field that accelerates light ions. The dependence of the maximum proton energy on the foil thickness has been found and the laser pulse characteristics have been matched with the thickness of the target to ensure the most efficient acceleration. Moreover the proton spectrum demonstrates a peaked structure at high energies, which is required for radiation therapy. 2D PIC simulations show that a 150-500 TW laser pulse is able to accelerate protons up to 100-220 MeV energies.