Stimulated Raman Sidescattering And Generation Of Attosecond Electron Beams In Laser-plasma Interaction

In the past 30 years,rapid progress of laser technology has promoted the researches of laser-plasma interaction.Many related physical problems,such as laser propagation in plasma,excitation of plasma wave,development of instability,have been deeply studied and made remarkable progress.At the same time,many important applications have been proposed,such as inertial confinement fusion,laser-driven particle source,laser-driven radiation source.In this thesis,some physical problems related to plasma wave in laser-plasma interaction are studied,which are mainly as follows:1.Stimulated Raman side scattering excited by intense laser in a plasma with a steep density gradient is studied both numerically and theoretically.With the development of ultra-short and ultra-intense laser,the instability in steep density gradient plasma has been paid more and more attention.The results of particle-in-cell simulation show that the strongly stimulated Raman side scattering eigenmodes are excited even if the plasma scale is as short as one laser wavelength.By studying the effect of the scale length on the properties of stimulated Raman side scattering,it is found that there is a minimum scale length to ensure that the scattered light is strong enough to be observed effectively,and the frequency of the scattered light is gradually approaching half that of the incident laser pulse.when the ion motion is not taken into account,the simulation results are in good agreement with the linear theory of stimulated Raman scattering growth in inhomogeneous plasma.It is shown that the linear theory is applicable to the growth of stimulated Raman scattering in a plasma with a steep density gradient.However,when the motion of the ions is considered in the simulation,the bending of the plasma caused by pondermotive force has an important influence on the properties of the scattered light.Even so,according to the characteristic of stimulated Raman side scattering in the plasma with steep density gradient,the range of short plasma density scale length can be qualitatively determined by.This is beneficial to the study of the interaction between laser and nano-film target.2.The generation of attosecond high-quality electron beam in crystal driven by relativistic x-ray laser is studied by 2D particle-in-cell simulation.As a new type of light source,x-ray laser has been developed rapidly and it is expected to obtain attosecond x-ray pulses of relativistic intensity in the near future.Relativistic intensity x-ray can excite a wakefield of the order of TV/cm in the crystal.Although the wakefield is periodically modulated by the electrostatic field near the lattice,the acceleration of electrons in the wakefield is not affected.Because of the stability of the crystal,the wave breaking at the sharp vacuum boundary of the crystal can lead to the injection of electrons into the cavity and this injection has a high repeatability.In addition,electron injection can be controlled by coating the crystals with nano-thin films of different densities.Thus,with the interaction of a relativistic x-ray laser and a micron-thick crystal clip,high energy attosecond electron beam with low emittance and low energy spread can be obtained.This compact crystal accelerator has a repetition frequency of MHz and sufficient control of electron beam parameters.In the future,it can be used as an ideal electron source for ultrafast electron diffraction and ultrafast electron microscopy with attosecond resolution.