Abstract
We present theoretical considerations on the process of ion acceleration with ultra-thin foils irradiated by elliptically polarized, highly intense laser pulses. Very recently the radiation pressure acceleration regime was predicted where mono-energetic ion bunches can be produced with high efficiencies (Klimo et al 2008 Phys. Rev. ST Accel. Beams 11 031301; Robinson et al 2008 New J. Phys. 10 013021). We have studied the process by means of 1D particle-in-cell (PIC) simulations and analytical models and have considered effects of areal mass density of the target and laser ellipticity on the ion acceleration process. For certain target densities and laser parameters the optimum target thickness has been extracted. Peaked ion spectra are found for ellipticity beyond a threshold value of about 0.7. Here, we highlight the drastic difference between linear and circular polarization by movie animations.
Highlights
We present theoretical considerations on the process of ion acceleration with ultra-thin foils irradiated by elliptically polarized, highly intense laser pulses
We have studied the process by means of 1D particle-in-cell (PIC) simulations and analytical models and have considered effects of areal mass density of the target and laser ellipticity on the ion acceleration process
For ξ 1, the laser pressure is stronger than the electrostatic pressure, and the electrons are pushed out of the target foil, whereas for ξ 1 compressed electrons and space charge field remain inside the foil, accelerating the ions layer by layer [14]
Summary
We assume a steady state of the interaction where the electrostatic pressure is balanced by the radiation pressure of the laser (see movie 1, available from stacks.iop.org/NJP/10/113005/mmedia). For ξ 1, the laser pressure is stronger than the electrostatic pressure, and the electrons are pushed out of the target foil, whereas for ξ 1 compressed electrons and space charge field remain inside the foil, accelerating the ions layer by layer [14]. The energy will be less when the 1D description breaks down, i.e. when the separation distance Ls approaches the diameter of the laser focal spot 2rL This would lead to a lower ion energy in equation (5) and may be described by replacing the laser pulse duration tL by the value 2rL/c; here the electrons are assumed to move with speed of light away from the ions given them a shorter time, i.e. 2rL/c to respond on the charge separation fields.
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