Theory And Numerical Simulations Of Interaction Between Composite Laser Fields And Plasmas

The study of interaction between composite laser field and matter has importantsignificance, because it’s about particle acceleration, novel radiation sources as well asthe laser pulse shaping and control applications. We have investigated the motion ofelectrons in linear polarization relativistic laser standing wave fields. The dependencesof scattering electron incident in laser polarization plane on the electron’s initialposition, energy as well as the laser intensity have been analyzed. Usingone-dimensional particle-in-cell simulations, the generation of a single attosecondpulse from an overdense plasma surface driven by ultra-relativistic laser(over1022W cm2) with time-dependent polarization is studied.We study the interaction of the electron and linearly polarized laser standing wave,using the relativistic Lorentz equations, discussion of the relativistic electrons incidentfrom different directions, in laser standing wave trajectory, energy changes andacceleration.The results indicate that the interaction between electron scattering andsanding wave has a close relationship with the electron relative energy0/a0. Theinitial energy of electron has a critical value by which the forward and backwardscattering can be distinguished. The critical energy needed for electron forwardscattering increase by the laser intensity. With electronic relative energy to measure,the critical value at about1.0-1.25range. For the same initial energy, the extent ofelectron incident plane leading the forward scattering reduce when the laser intensitygets higher. Moreover, electrons with low energy easily tend to pass through thestanding wave from node planes. Electron oscillation-center and Ponderomotive forcereversal effect exist merely when the electron relative energy is in a certain range. Theelectron initially rest on optical axis and the inelastic scattering in which the energycan be exchanged between the electron and the field are also discussed.Using one-dimensional particle-in-cell simulations, the generation of a single attosecond pulse from an overdense plasma surface driven by ultra-relativistic laser withtime-dependent polarization is studied. Due to the difference of the electron-ion mass,so that the reaction of the electronics of the laser is much faster than the ions. In thesimulation, slow ion movement can be ignored temporarily. We only consider theelectron motion. Simultaneously improving the amplitude of the driving pulse and thecontrolling pulse, we can see that the conversion ratio of attosecond pulse has aincreasing trend. Because of that the increase of the corresponding target density makesthe number density of the oscillation electron greatly improved and it makes theattosecond pulse conversion ratio significantly larger than that under the relativisticintensity laser. Under ultra-relativistic intense laser, the ion motion effects becomeimportant. The motion of ions breaks the regular and stable oscillation of the electron onthe plasma surface. This will affect the conversion ratio of the attosecond pulse. Wecompared the impact of different target materials on attosecond pulses. We get thatheavy target material gets higher conversion ratio attoscond pulses. When the laserpulse intensity is too large compared with dense plasma target density, laser goesthrough the plasma target directly, and the oscillation model of the target surface isdestroyed. We can’t get a single attosecond pulse.The thesis is organized as follows. The first chapter gives a brief introduction ofdeveloping process of laser technique, the interaction of laser pulse with plasma and thegeneration of high-order harmonics and attosecond pulses. In the second chapter, weshow the theoretical model of high harmonics generation. Then, in the third chapter,scattering of electrons in linearly polarized high-intensity laser standing waves is studied. In chapter four, using one-dimensional particle-in-cell simulations, thegeneration of a single attosecond pulse from an overdense plasma surface driven byultra-relativistic laser (over1022W cm2) with time-dependent polarization is studied. Asthe conclusion, in the last chapter, we briefly summarize the total subject and give anexpectation for the future work.