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ION ACCELERATION IN LASER IRRADIATED SMALL-SIZE TARGETS

by Sophie Heurtebise - published on

Jeudi 6 mars 2008

Ion acceleration by femtosecond laser pulses has been studied theoretically by means of particle-in-cell simulations. This presentation covers two basic topics: a) Ion acceleration by femtosecond laser pulses in mass-limited multispecies targets, b) Monoenergetic ion beams from ultrathin foils irradiated by circularly polarized laser pulses. Each of those phenomena is based on different ion acceleration mechanism.

When a p-polarized intense laser pulse irradiates a small-size ionized target (overdense plasma), a population of hot electrons with a very high temperature Th is formed. These hot electrons cross the target and propagate beyond its rear side. There, a sheath layer is formed and a strong electrostatic field accelerates ions. Mass-limited targets, which are of comparable sizes with laser focal spot, limit the spread of hot electrons in the transverse direction. Thus, with increasing hot electron density nh, an enhancement of the sheath field and the following increase of the energy of accelerated ions is expected. Mass-limited targets of various shapes consisting of two ion species are considered. Their energy spectra and divergence of ion beams are compared for the same laser pulse parameters.

When a circularly polarized intense laser pulse irradiates an ultrathin foil, a compact plasma slab can be accelerated under certain conditions. In this case, strong electron heating is undesired, because it disturbs the compactness of the plasma block. This acceleration mechanism works well in 1D analysis, but in 2D has many constraints which are also presented.

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