Observation of proton modulations in laser–solid interaction

Abstract We report on an experimental investigation into proton acceleration from the interaction of an intense laser pulse, with an intensity of about 10 20 W cm −2 , with a thin foil of aluminum, titanium and gold of thickness 2 µ m. Protons are accelerated via the TNSA mechanism from the rear surface of the target and, in addition, protons accelerated from the front surface are also detected on the radio chromic films. Hollow proton rings could be seen on the radio chromic films, corresponding to 1–3 MeV protons. The protons from the front surface are driven into the target and directed towards the rear side of the target by the Kilotesla magnetic fields generated from the laser plasma. 2D particle-in-cell simulations predict an increase in the flux of lower energy protons similar to experimental observations and also show strong magnetic field structures in the laser–target interaction region.