Experimental Studies On High-energy Particles Produced During The Interaction Of Ultrashort Ultra-intense Laser Pulse With Plasma

Angular distribution and energy spectrum of the high-energy particles produced during the interaction of ultra-short ultra-intense (US-UI) laser pulse with plasma are studied in this paper. As the laser intensity is about ~1018W/cm2, we obtained some new results from the interaction of the US-UI laser pulse with plasma that have not been reported before in China. These results are helpful to understand the physical mechanisms of the laser-plasma interaction, and are very important for the research of fast ignition (FI) for inertia! confinement fusion (ICF).The development of the laser technology, the progress of the interaction of the US-UI laser pulse with plasma (Physics of Intense Field), and the research of the fast ignition are firstly introduced. Secondly, the basic concepts and theories for thelaser-plasma interaction are expatiated and the absorption of US-UI laser by solids or overdense plasma, the experiment results, theory, and computer simulation for high-energy particles are discussed in detail. The experiment setups at the Laser Fusion Research Center in China Academy of Engineering Physics (CAEP) are also introduced. Finally, the introduction is focused on the experimental results of the angular distribution and the energy spectrum of the hot elections emission and the energetic prlSton emission during the interaction of the US-UI laser pulse with plasma.In this paper, such three points are studied as: a) the angular distributions of the hot electrons emission under laser irradiation at different incidence angles and atdifferent polarization direction, the angular distribution of the hot electrons in the different energy range, and the effects of laser prepulse on the angular distributions of the hot electrons emission; b) the energy distribution of the hot electrons at different directions, from the metallic targets and the dielectric targets, in the different energy range of the hot electrons, and the effects of the atomic number Z on the energy distribution of hot electron generated by the metallic targets; and c) the energetic proton emission resulting from the interaction of the US-UI laser pulse with plasma.In the investigation of the interaction of the US-UI laser pulse with the plasma, a standard -ray source is firstly used to absolutely calibrate LiF mermc-luminescence dosimeters (TLDs), and the dosimeter are employed as the angular distribution spectrometer and the energy spectrum spectrometer of the hot electrons. Angular distribution and energy spectrum of the hot electrons emission resulted from the interaction of the US-UI laser pulse with plasma are measured with the calibrated LiF TLDs, and the yield of the hot electrons is consistent with the results of the other experiments.In the experiment of the angular distribution of the hot electrons emission, three-peaks and double-peaks emission of the hot electrons resulted from the multi-acceleration mechanisms are observed in our experiments. These emission peaks are located in the directions of the specular reflection of laser, the target normal and the back-reflection of laser respectively. The peak in the direction of the target normal is consistent with mat of predicted by the resonance absorption and another peak of hot electrons emission in the specular reflection direction is due to the multi-acceleration mechanisms. The hot electrons emission along the back-reflection direction is probably caused by the acceleration of the back-reflection laser, which is for the first time put forward by us. The experimental results are helpful to understand the acceleration mechanisms of the hot electron emission in the interaction of the US-UI laser pulse with plasma.An anisotropy energy distribution of the hot electrons emiAon has been observed for the first time in the experiments. The energy spectrum of hot electrons resulted from the resonance absorption at the direction of target normal is a Maxwellian-like distribution. Fitting the spectrum with MaxweUian distribution, theeffective temperature of about 200keV...