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We have theoretically investigated the acceleration of ions in the interaction of high intensity, circularly polarized laser pulses with overdense plasmas. By using 1D and 2D particle-in-cell (PIC) simulations we find that high-density, short duration ion bunches moving into the plasma are promptly generated at the laser-plasma interaction surface. This regime is qualitatively different from ion acceleration regimes driven by fast electrons, such as sheath acceleration at the back of the target or shock acceleration at the front, which occur for linear polarization. A simple analytical model accounts for the numerical observations and provides scaling laws for the ion bunch velocity and generation time as a function of pulse intensity and plasma density. The present mechanism based on circular polarization of the laser pulse leads to moderate ion energies (in the 100 keV–1 MeV range) but very high ion densities and low beam divergence. These ion bunches might be of interest for problems of compression and acceleration of high-density matter by short pulses as well as for the development of compact neutron sources. We analyzed a scheme based on two-side irradiation of a thin foil deuterated target, where two colliding ion bunches are produced leading to an ultrashort neutron burst. We evaluated that, for intensities of a few 1019 W cm-2, more than 103 neutrons per Joule may be produced within a time shorter than one femtosecond. Another scheme based on a layered deuterium-tritium target is outlined. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

The interaction of short, relativistic laser pulses with a cold overdense plasma is investigated using computer simulations based on a fluid code. Depending on the background plasma density, two qualitatively different scenarios were observed for the penetration of the laser pulse, which is normally incident onto an overdense plasma. The first scenario is realized at moderate values of the background density (N[sub 0]<1.5N[sub cr], where N[sub cr] is the critical plasma density) and implies a dynamic regime with moving soliton-like structures, which penetrate deeply into the plasma. The second one takes place at higher densities (N[sub 0]>1.5N[sub cr]) and the laser radiation penetrates over a finite length only. As long as we can neglect the ion motion, in this regime the plasma-field structures consist of alternating electron layers separated by cavities of about half a wavelength with strong charge separation. When the effects of ion motion become significant, the electron slabs are squeezed by ions with formation of a plasma shock wave. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]