The Interaction Of Ultrashort Intense Laser Pulses With Plasmas

In recent years,with the development of Chirped Pulse Amplification technique, laser pulses with focused intensities I≈1018-22W/cm2 and pulse widthτ<1ps are available in many laboratories. The study of the interaction of ultrashort intense laser pulses with plasmas,which is motivated primarily by the fast ignition scheme of inertial confinement fusion,has received more and more attention. This thesis is devoted to studying those issues relevant to the interaction of ultrashort intense laser pulses with plasmas.We study self-compression and splitting of a circularly polarized laser pulse propagating in plasmas with its density window from 1/4 critical to slightly below critical density by solving the nonlinear Schrodinger equation numerically. It is demonstrated from the numerical calculation that effective self-compression of laser pulse can be achieved in even shorter distance by increasing both the background plasmas density and intensity of the laser pulse, or decreasing the width of pulse. The full-width at half maximum of the compressed pulse can reach even 1/35 of the initial one's, and even smaller. It has been found that this kind of self-compression appears in the process of formation of a high-order soliton when a laser pulse propagates in plasmas, so that we can gain more effective compression ratio than that in thin plasmas. We also obtain the splitting of a high-order soliton formed after self-compression of a laser pulse propagating in plasmas from the result of the numerical calculation in this kind of situation. The phenomenon of self-compression and splitting is also observed by using one-dimension particle-in-cell simulations and we get the consistent result with the numerical calculation.Solutions of electron and ion density gratings at the linear stage are given. Deep plasma gratings produced by the ponderomotive force of the interference of the two intersecting laser pulses are investigated. Dependence of the plasma gratings on the plasma densities, durations and intensities of the laser pulses are studied with 1D Particle-in-cell (PIC) simulations. It is found that the density peaks of such gratings can be 8 times of the initial plasma density and last a few picoseconds.Consider two counter-propagating laser pulses in plasmas, the interaction between the pulses and plasma creates modulation of the electronic and ionic density in plasmas and leads to the Stimulated Raman scattering instability and then results in the localized stable, long-living entities called relativistic electromagnetic solitons. The laser pulses experience stimulated Raman scattering instability and a part of the scattered electromagnetic energy is trapped inside an empty density cavity in which there almost not exist any plasma substantial, therefore allows for trapping relativistic electromagnetic solitons. Dependence of the formation of relativistic electromagnetic solitons on the ion motion, plasma temperature and length, plasma densities, intensities and durations of laser pulse are studied by particle-in-cell simulations.The thesis is organized as follows. The first chapter gives a brief introduction of research background and developing process of interaction of laser pulse with plasma. In the second chapter, we investigate self-compression and splitting of laser pulse in plasmas. Then, in the third chapter, Plasma Bragg gratings generated in the interaction of two counter-propagating laser pulses with plasmas is explored.Chapter four presents our result of the formation of relativistic electromagnetic solitons with plasma Bragg gratings induced by two counter-propagating laser pulses. As the conclusion, in the last chapter, we briefly summarize the total subject and give an expectation for the future work.