Experiment And Simulation Study On Ion Acceleration In Ultrashort Ultraintense Laser-Plasma Interactions

The thesis is focused on the acceleration of energetic ion beams in laser-foil interactions. It’s composed of three parts:First, the origin of energetic carbon ions with different charge states in laser-thin foil interactions. Second, the experiment study of ions, which accelerated from the target normal direction in ultrahigh intensity laser-foil interactions. Lastly, the interactions of ultra-intense circularly polarized laser with a mixed solid target are studied by two-dimensional (2D) particle-in-cell (PIC) code, and high energy(-GeV) protons are founded.The first part is devoted to the ionization mechanisms in the laser-solid interactions. It’s mainly consisted of direct ionization by the laser pulse, field ionization by barrier suppression (FIBS) and collisional ionization (CI) by the ambient electron populations. Then, the origin of the ions is studied by analyzing the basic ionization processes occurring at the rear surface. It is shown that the normally dominant ionization processes is "Field lonization by Barrier Suppression"(FIBS) for charge states less than He-like(C4+), while "collisional ionization"(CI) is significant for C5+and C6+.The second part shows the experiment results of laser-foil interactions on the Xtreme Light Ⅲ (XL-Ⅲ) laser system at the Institute of Physics, Chinese Academy of Sciences. Fristly, we found that the optimum thickness for proton acceleration is2.5μm, and the maximum cutoff energy is3.9MeV. We estimated the area of lateral dispersion and divergence angle of hot electrons via TNSA mechanism. It shows that they both dependent the variation of target thickness. Secondly, we combined with the ionization mechanisms in chapter2, and studied the effect of target thickness for accelerated carbons with different charge states. Thirdly, a two-temperature electron distribution was observed in our experiment, and we simply explaied this observation.The third part is mainly about the effect of mixed target composition parameters on proton acceleration in ultra-intense laser-thin foil interaction. We found that the density ratio n between the protons and carbon ions plays an important role in determining the acceleration process. For a mixed target, a relatively low proton density gives rise to peaks in the energy spectrum, and quasi-monoenergetic high energy protons are generated through the normal RPA mechanism. But for a large n value, a proton beam with high maximum energy and wide energy spread could be generated.