Fast ion generation from nanostructure target irradiated by high intensity short laser pulse

摘要

One of problems of physics of laser particle acceleration is increase of transformation of laser pulse energy in particle kinetic energy. Changing parametres of a laser target, it is possible to operate such ion characteristics as the maximum and average ion energy, angular divergence and spatial distribution. Rather recently [1], it was revealed, that transformation of laser energy in ion energy increases at use a thin foils limited in size. Occupying smaller effective volume hot electrons have higher density and temperature, accelerating ions more effectively. There is an optimum range for target thickness since too thin targets lead to a warming up a thermal wave of borders of a target, and too thick to electron energy losses. Optimization of some targets under geometrical characteristics was made, for example in [2]. The absorption of laser radiation of such targets reaches considerable values, however are not 100 %. In paper [3] using a periodic micro-relief on a target surface has been shown, that, it is capable to increase absorption of laser radiation up to 90 %. In the present paper it is offered to increase in such way absorption of thin targets and to choose parameters of a relief and basic part of a target so that the additional absorbed energy is transferred mainly to the accelerated protons. The choice of optimum characteristics of a target is made by means of analytical and numerical PIC modeling of a target set with characteristics near to optimum values. The calculations have shown that there is no necessity for ideal periodicity and a regularity of target relief for essential growth of absorption and energy of a proton. Replacement of a regular relief on randomly rough with characteristic scale comparable with regular considerably does not reduce neither absorption, nor energy of the accelerated ions.