MeV proton acceleration at kHz repetition rate from ultra-intense laser liquid interaction

Abstract

Laser acceleration of ions to ≳MeV energies has been achieved on a variety of Petawatt laser systems, raising the prospect of ion beam applications using compact ultra-intense laser technology. However, translation from proof-of-concept laser experiment into real-world application requires MeV-scale ion energies and an appreciable repetition rate (>Hz). We demonstrate, for the first time, proton acceleration up to 2 MeV energies at a kHz repetition rate using a milli-joule-class short-pulse laser system. In these experiments, 5 mJ of ultrashort-pulse laser energy is delivered at an intensity near $5\times {10}^{18}\,{\rm{W}}\,{\mathrm{cm}}^{-2}$ onto a thin-sheet, liquid-density target. Key to this effort is a flowing liquid ethylene glycol target formed in vacuum with thicknesses down to 400 nm and full recovery at 70 μ s, suggesting its potential use at ≫kHz rate. Novel detectors and experimental methods tailored to high-repetition-rate ion acceleration by lasers were essential to this study and are described. In addition, particle-in-cell simulations of the laser–plasma interaction show good agreement with experimental observations.

Keywords

• ion acceleration
• MeV proton acceleration
• laser–plasma interaction
• ultra-intense laser solid interaction
• target normal sheath acceleration
• particle-in-cell