Proton beam quality enhancement by spectral phase control of a PW-class laser system

Abstract

We report on experimental investigations of proton acceleration from solid foils irradiated with PW-class laser-pulses, where highest proton cut-off energies were achieved for temporal pulse parameters that varied significantly from those of an ideally Fourier transform limited (FTL) pulse. Controlled spectral phase modulation of the driver laser by means of an acousto-optic programmable dispersive filter enabled us to manipulate the temporal shape of the last picoseconds around the main pulse and to study the effect on proton acceleration from thin foil targets. The results show that applying positive third order dispersion values to short pulses is favourable for proton acceleration and can lead to maximum energies of 70 MeV in target normal direction at 18 J laser energy for thin plastic foils, significantly enhancing the maximum energy compared to ideally compressed FTL pulses. The paper further proves the robustness and applicability of this enhancement effect for the use of different target materials and thicknesses as well as laser energy and temporal intensity contrast settings. We demonstrate that application relevant proton beam quality was reliably achieved over many months of operation with appropriate control of spectral phase and temporal contrast conditions using a state-of-the-art high-repetition rate PW laser system.

ReLaX: the Helmholtz International Beamline for Extreme Fields high-intensity short-pulse laser driver for relativistic laser–matter interaction and strong-field science using the high energy density instrument at the European X-ray free electron laser facility

“…ReLaX is a standalone laser system based on the Pulsar 500 HR product series of Amplitude Technologies France and similar to other Ti:Sa systems [25][26][27][28][29] . It was delivered and installed in 2018 on site at EuXFEL.…”

Effects of pulse chirp on laser-driven proton acceleration

“…A modification of this approach is to alter the temporal profile of the main pulse itself. Recent numerical 21 , 22 and experimental 23 , 24 works have demonstrated that deviations from an ideal Fourier transform-limited pulse can lead to an increase of the cut-off energies of the laser-accelerated protons. However, there are still ambiguities about which pulse shape, and the related absorption process, optimises the proton acceleration.…”

High Efficiency Laser-Driven Proton Sources Using 3D-Printed Micro-Structure

“…These sub-100MeV protons are obtained by relatively long laser pulses of 100's J energies. For femtosecond lasers, typical cutoff energy of protons lies in 30-70 MeV using planar targets [9][10][11] , since the pulse energy is usually much less than picosecond lasers.…”