Experimental Studies Of Proton Generated By Laser-plasma Interaction At The Rear Side Of Target

During the interaction of ultra-short and ultra-intense pulse laser with plasma, energetic proton beams will emit in the form of pulse. Especially, the protons that emit in a samll cone angle in the direction of target normal have some excellent advances, such as small source size , short pulse duration and high degree of collimation which will enable those protons be applied widely in ion acceleration,proton imaging,"fast ignition",therapy cancer and etc. So this thesis mainly studies the experiments of protons emitting in the interaction of ultra-short and ultra-intense pulse laser with plasma at the rear side of target, in particular paid attention to the characteristics of the protons emitting in the target normal direction , including the relation of the spatial distribution, the energy distribution ,targets and laser intensity.Firstly, the thesis simply introduces the model and significances of the fast ignition, and the research development of the protons produced in the interaction of ultra-short and ultra-intense pulse laser with plasma. Secondly, we expatiate in detail the theory of three aspects: the process of the interaction of laser with plasma; the process of the interaction of the ultra-short and ultra-intensity laser with plasma; and the acceleration mechanisms of protons. At last and most importantly, we introduce the experimental research, and then analyze and discuss the results.Our experiments are carried out at the ultra-short and ultra-intense laser facility in the China Academy of Engineering Physics. In the experiments, we use radiochromic film to detect space distribution of proton; CR39 and Thomson ion spectrometer to measure the energy spectrum of the protons. We measure the space distribution of protons along the target back normal direction.Then we draw a conclusion that the emitting angle is about 51°and isn,t relation with laser spot.When we use the double plane target ,the hollow,disc and filament space distribution of protons are detected.With the thickness of target increasing,the number of protons decrease. When CR39 used to detected the energy of protons, 1.2mm diameter round shape is detected in CR39 center. Because the round shape matters don,t sense magnetic and electric field,so the round shape matters are made up of neutral ions and energetic photons. Energetic protons pass through magnetic and electric field of Thomson ion spectrum, then different energy protons form a parabola. The round shape center as dot,we read coordinate and number of protons. According to caculation, we draw the protons energy spectrum. When protons energy increaing, the number of protons are decreased. Through fitting exponential decay ,we find the fitting is in good agreement the experiment result, so we draw a conclusion the proton energy spectrum is exponential decay.In the proton energy spectrum,there is a cut-off energy. The proton cut-off is increased with the laser intensity when we use the same thickness 7μm Cu targets. The proton cut-off energy of 7μm Cu target is 1.385MeV,but the proton cut-off energy of 5μm Cu target is 663keV which is small. When we use double target,the number of protons increase,but protons energy don,t increase dramatically. All results were in good agreement with the acceleration mechanisms of protons and other experiment results.