Electron Acceleration And The Generation Of Attosecond Electromagnetic Emission In Laser-plasma Interaction

Electron acceleration is a basic physical process in the interaction between the relativistic laser and plasma foil targets,and it is the basis of the other physical phenomena.When the electrons move in a plasma foil target driven by the relativistic laser pulse,they emit the attosecond electromagnetic?EM?pulses through different mechanisms due to the efforts of the electromagnetic field.However,the research on electron acceleration and electromagnetic radiation is isolated,and the detailed process and generation mechanism of the attosecond EM pulses associated with the wavebreaking is still lacking.Thus,we combine the EM emission with the wavebreaking of the plasma foil target and electron acceleration.The electron acceleration and generation of the attosecond EM pulses associated with the wavebreaking phenomenon in the interaction of relativistic laser pulse with dense plasma foil target are investigated in detailed by using partical-in-cell?PIC?simulations.The current research background,the status of the electron acceleration mechanisms and the EM emission mechanisms are respectively introduced at the beginning of this paper.Then,the theoretical basis of the plasma is given,including the definition,the independent parameters,the classification,the research methods,the plasma wavebreaking and self-injection,the basic equations of EM emission,and the theory of the EM emission mechanisms.The PIC simulation used in our research is also introduced in detail in this paper,including the methods and basic process of the PIC simulation,solving the particle motion equations,solving the EM fields,solving the charge density and current density.Next,we give the simulation parameters and results we needed and analysis them in detail.The characteristics of the transverse electric field and longitudinal electric field,the characteristics of the emitted attosecond EM pulses,the time when the attosecond EM pulses emission occur,the generation mechanisms of the attosecond EM pulses,the emission process of the electrons and the energy conversion efficiency,etc.are analyzed.The effect of the Carrier Envelope Phase?CEP?and the intensity?₀a?of the driving pulse on electron acceleration and EM emission are also discussed.The generation of attosecond EM pulses and associated electron dynamics are studied by using PIC simulations of relativistic laser pulses interacting with over-dense plasma foil targets.The interaction process is found to be so complicated even in the situation of utilizing driving laser pulses of only one-cycle.Two electron bunches closely involved in the laser-driven wavebreaking process contribute to attosecond EM pulses through the Coherent Synchrotron Emission?CSE?process whose spectra are found to follow an exponential decay rule.Detailed investigations of electron dynamics indicate that the early part of the reflected EM emission is the high-harmonics produced through the Relativistic Oscillating Mirror?ROM?mechanism.High-harmonics are also found to be generated through the Bremsstrahlung radiation by one electron bunch that participates the wavebreaking process and decelerates when it experiences the local wavebreaking-generated high electrostatic field in the moving direction.In addition,an electron bunch not participates in the process of wavebreaking can be accelerated to the speed close to c?the speed of light in the vacuum?,and emit an attosecond EM pulse in the reflected direction through the CSE mechanism.The effect of the parameters of the driving pulse on the electron acceleration and EM emission indicate that the larger the CEP of the driving laser is,the later the time when the wavebreaking occurs is,and the location where the wavebreaking occurs is deeper in the plasma target.The density of the wavebreaking point increases first and then decreases with the increase of the CEP.In the case of CEP?28??4,the value of electron density of the wavebreaking point is the largest.For the emitted attosecond EM pulses,the larger the CEP is,the higher the intensity of the attosecond EM pulses is,the smaller the number is and the smaller the CEP is,the lower the intensity of the attosecond pulses is,the larger the number is.The intensity of the driving laser pulse almost has no effect on the time when the wavebreaking occurs.The position of the wavebreaking point is deeper in the plasma target as the amplitude increases,and the density of the wavebreaking point increases first and then decreases.In the case of a₀?28?25,the density reach the maximum.Under the condition of the plasma target is not broken down,the larger thea₀ is,the higher the intensity of the EM pulses is and the larger the number is.More simulations are performed to show the effect of the two parameters on the intensity of the emitted attosecond pulses,as determined that the intense attosecond pulses are obtained with the CEP in the range of-0.8⁰ and2.4³.0,anda₀ should be greater than 20.