The Spanish Pulsed Laser Centre (CLPU) is a new high-power laser facility for users. Its main system, VEGA, is a CPA Ti:Sapphire laser which, in its final phase, will be able to reach petawatt peak powers in pulses of 30 fs with a pulse contrast of 1 : 10¹⁰ at 1 ps. The extremely low level of pre-pulse intensity makes this system ideally suited for studying the laser interaction with ultrathin targets. We have used the particle-in-cell (PIC) code OSIRIS to carry out 2D simulations of the acceleration of ions from ultrathin solid targets under the unique conditions provided by VEGA, with laser intensities up to 10²²Wcm^-2 impinging normally on 5 - 40 nm thick overdense plasmas, with different polarizations and pre-plasma scale lengths. We show how signatures of the radiation pressure dominated regime, such as layer compression and bunch formation, are only present with circular polarization. By passively shaping the density gradient of the plasma, we demonstrate an enhancement in peak energy up to tens of MeV and monoenergetic features. On the contrary linear polarization at the same intensity level causes the target to blow up, resulting in much lower energies and broader spectra. One limiting factor of Radiation Pressure Acceleration is the development of Rayleigh-Taylor like instabilities at the interface of the plasma and photon fluid. This results in the formation of bubbles in the spatial profile of laser-accelerated proton beams. These structures were previously evidenced both experimentally and theoretically. We have performed 2D simulations to characterize this bubble-like structure and report on the dependency on laser and target parameters.

Date Published: 14 May 2015
PDF: 9 pages
Proc. SPIE 9514, Laser Acceleration of Electrons, Protons, and Ions III; and Medical Applications of Laser-Generated Beams of Particles III, 95141D (14 May 2015); doi: 10.1117/12.2178522

Published in SPIE Proceedings Vol. 9514:
Laser Acceleration of Electrons, Protons, and Ions III; and Medical Applications of Laser-Generated Beams of Particles III
Kenneth W. D. Ledingham; Eric Esarey; Carl B. Schroeder; Klaus Spohr; Paul McKenna; Florian J. Grüner; Paul R. Bolton, Editor(s)