Energetic proton production from relativistic laser interaction with high density plasmas

Abstract

Energetic protons up to 30 MeV have been measured from high intensity laser interactions (⩽5×1019 W/cm2) with solid density plasmas. Up to 1012 protons (> 2 MeV) were observed at the rear of thin aluminum foil targets and measurements of their angular deflection were made. Similar energies were measured from ions produced from the front of the foils. Nuclear activation and track detector measurements suggest that the protons measured at the rear originate from the front surface of the target and are bent by large magnetic fields that exist in the plasma interior, which are likely generated by a laser-produced beam of fast electrons.

High-energy ion generation in interaction. of short laser pulse with high-density plasma

“…We found that the theoretical dependences of the ion-generation efficiency versus laser intensity and plasma profiles agree well with recent experiments at the Center of Ultrafast Optical Science at laser intensities of I ≤ 6 × 10 18 W/cm 2 [5] and the data on maximum ion energies from the experiments performed at the Rutherford Appleton Laboratory on the Vulcan laser [13].…”

“…The results obtained from some experiments [5,13] provide evidence that the observed MeV-ions were generated and accelerated in the plasma at the front of the target, conflicting with experiments [3,23] that indicated that proton acceleration took place at the back of the target. The electrostatic model of ion acceleration suggests that the origin of the ions is the same for both of these experiments and that the only difference is in the plasma thickness: whether or not the plasma extends to the rear surface.…”

“…The commonly recognized effect responsible for ion acceleration is charge separation in the plasma due to high-energy electrons, driven by the laser inside the target [1,3,12,13] and/or an inductive electric field resulting in the self-generated magnetic field [14], although a direct laser-ion interaction has been discussed for extremely high laser intensities ~ 10 22 W/cm 2 [8]. These electrons can be accelerated up to multi-MeV energies due to several processes, such as stimulated forward Raman scattering [15], resonant absorption [16], laser wake fields [17], ponderomotive acceleration by standing [18] and propagating [12] laser pulses, "vacuum heating" due to the v × B component of the Lorentz force [19] or the Brunel effect [20], wave-breaking of self-modulated laser wake fields or injection via wavebreaking of Raman-backscattered plasma waves [21], and betatron resonance provided by laser-pulse channeling [22].…”

Focusing of laser-generated ion beams by a plasma cylinder: Similarity theory and the thick lens formula

“…Laser-driven ion sources [1,2,3,4,5,6,7] are considered to be the hot candidates for various important applications in nuclear physics, medicine, biology, material sciences, plasma field tomography [8,9,10]. When multiterawatt laser pulses are shot on solid state targets, copious amounts of multi-MeV ions -both protons and highly charged heavier ions -are generated [11].…”

3/2 Harmonic Generation by Femtosecond Laser Pulses on Solid Targets

“…Experiments at this intensity level are of great interest because of a number of applications such as fast ignition [1], particle acceleration [2][3][4], hard x-ray [2][3][4] and high order harmonic generation [5], etc. Plasma instabilities can play an important role in these interactions.…”