| Particle acceleration, using ultrahigh-intensity laser-produced plasmas, has become a very interesting area of investigation in recent years. The electrostatic field established by the charge separation from a laser-induced ponderomotive force has the ability to drive particles from the plasma out into the vacuum. This simple laser and plasma particle accelerator setup can significantly reduce the size and cost compared to the conventional accelerators. More specifically, proton acceleration from solid targets has very good prospects for various applications. However, some of these applications would require higher proton energy or greater flux or smaller emmitance proton beam from the accelerator. For these reasons, the optimization and control of laser-plasma interactions are becoming very important topics of study at the present time.; Many previous publications have suggested that the preplasma introduced by a laser prepulse is key to the efficiency of proton acceleration. However, a clear relationship between preplasma expansion scale and proton acceleration efficiency has not yet been thoroughly investigated. This thesis provides a study of the optimization of preplasma produced by the ultrahigh-intensity-laser prepulse on solid targets. This experimental measurements of the angular distribution of fast electrons, electron beam close to laser on-axis direction and electrons along target tangential direction, provide the basis for obtaining the electric potential changes and the magnetic field generated by the ultrahigh-laser pulse and solid target interactions. With the understanding of electron distribution and the prepulse optimum condition, a thorough proton acceleration mechanism can be plotted.; Besides prepulse and electron distribution study, a proton beam spatial profile and energy spectrum are fully studied in my thesis. Conductors can provide a higher and smoother proton beam from laser-plasma interactions than insulators. Together with the acceleration origin study, this thesis provides good evidence of "Modified TNSA mechanism," which predicts that lower-energy protons are from front side acceleration and higher-energy protons are from rear side acceleration.; My research explores improving the efficiency of the proton acceleration, which involves the movement of electrons. Specifically, the electrical field potential generated from the electrons is the key to driving the protons. This thesis documents three factors that affect the movement of electrons: solid target materials, incident laser intensity, and the intensity peak-to-peak contrast ratio of the laser pulse. By studying the effect of these factors, an optimum condition of the proton acceleration can be found. |
