Ionization Dynamics in Intense Laser-Plasma Interaction

Recently, laser-accelerated ion beams from the back of solid targets have been observed in petawatt laser experiments, showing high levels have been observed in petawatt laser experiments, showing high levels of beam intensity and low emittance. Experiments and previous numerical modelling suggest that these ions are produced by sheath acceleration off the rear surface of laser-irradiated targets; they are ionized and accelerated by quasistatic electric fields that are due to an expanding cloud of hot electrons coming from the front side of the targets. 

We investigate the ionization dynamics in these targets by means of one-dimensional particle-in-cell (1D-PIC) simulations including collisions, ie. collisional ionization  as well as binary collisions between particles, in addition to the usual field ionization models [1]. Our aim is mainly to understand from where in the target the different ion species, ie. charge states, originate in order to manipulate ion beam spectra at an early stage.  

We further investigate the subsequent acceleration of the ions, paying special attention to the role of contaminants on the target's back surface. Our past results show good  agreement with experiments by Hegelich [2], giving  qualitatively identical features in the ion spectra. In the late acceleration stage we find good agreement between PIC simulations and self-similar solutions for the quasi-neutral expansion of plasma mixtures into vacuum [3].

[1] R.Pfund, PhD Thesis, TU München (1999)
[2] M. Hegelich et al., Phys. Rev. Lett. 89, 085002 (2002),   
[3] A.V. Gurevich and A.P. Meshcherkin, Sov.Phys. JETP 53, 937 (1981)

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latest change: 06/08/02, by A.Kemp

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