Theoretical investigation of the interaction of ultra-high intensity laser pulses with near critical density plasmas

A theoretical model of energy transfer from laser to particles in the ultra-high intensity regime of laser plasma interaction is proposed, assuming that most of the laser energy will be transferred to hot electrons. Varying the target density and thickness, the optimal parameters for the maximum conversion efficiency of the laser energy to particles are studied. Through 2D particle-in-cell simulations, the model is validated for a near-critical density plasma between 0.5 - 20n(c) (where n(c) = 1.1 middot 10(21) cm(-3) is the critical density for a laser wavelength of lambda = 1 mu m) irradiated by a laser pulse of intensity in the range 10(20)-10(23) W cm(-2 )and the pulse duration in the range 6.5-100 fs. As an application to this model, laser ion acceleration is studied for a laser intensity of 10(22) W cm(-2) and a pulse duration of 20 fs. Based on the literature and new findings from our model, the optimum thickness for ion acceleration and the maximum ion energies for an expansion like mechanism are predicted. These results can be used for applications requiring high energy ions and for preparations of experiments at the Apollon and ELI laser facilities.