Particle In Cell Simulation Of The Dynamics For Intense Laser Induced High-pressure Generation And Plasma Gratings

Since the world's first laser became available in 1960,the laser technology has un-dergone rapid development,from Q Switching and Mode Locking in 1960s to Chirped Pulse Amplification(CPA)in 1980s and Optical Parametric Chirped Pulse Amplifica-tion(OPCPA)in 1990s.The laser intensity has increased from 104?105 W·C cm-2 to 1023 W·cm-2 during this period.The laser pulse meanwhile has been compressed from nanosecond order of magnitude to femtosecond.The advancement of laser technology has provide strong experimental support to the study of the interactions between lasers and materials.When intense laser pulses are used,there could happen abundant physical phe-nomena,such as multiphoton ionization,relativistic self-focusing,vacuum heating,anomalous skin effect,laser induced plasma transparency,wake fields in plasma,high order harmonic generation,x ray generation,production of electron-positron pair and so on.Especially,the investigating of the Laser plasma interaction has wide appli-cation in many fields,such as laser loading upon solids for high-pressure generation,plasma wake field acceleration,inertial confinement fusion,coherent ? ray sources and so on.In this thesis,we will use Particle In Cell(PIC)simulation method to study the following subjects:1.Evolution of plasma pressure driven by strong picosecond laser pulses.Based upon the so=called,"energy compression mechanism(ECM)",we have optimized the laser and plasma parameters to achieve the pressure as high as TP order of magnitude at the target rear surface.It is demonstrated that there are four stages in generating the high pressure.(1)The laser fields transfer the energy to the electrons;(2)Process of energy transferring from front surface to rear surface;(3)The ions are heated;(4)Process of unloading.Numerical results show that the peak value of the pressure is determined mainly by ions.2.Dynamics of the plasma grating induced by two counter-propagating ultra-violet fs laser pulses with the wavelength ? = 0.266 ?m and the plasma critical density nc = 1.5758 × 1028 m-3.When the plasma density is high,for example n0 = 4.25 × 10-2nc,the plasma grating is Steady Plasma Grating(SPG).When the plasma density is low,for example n0 = 4.25 × 10-4nC,the plasma grating is Os-cillatory Plasma Grating(OPG).In SPG the particle density has periodic in space dimension while in OPG the electron density is periodic in both space and time di-mension.The electron-ion interatins plays an important role in forming the two types of plasma grating.When the interactions are strong,the ions to move synchronously.For OPG,the interactions are weak and the ions are motionless.Moreover,in the long time evolution,hot electrons are observed in OPG.3.Interaction between intense infrared lasers and plasma gratings.(1)For ap-propriate incident laser intensity(eg.I = 1 × 1014 W·cm-2),the infrared laser pulse can enhance the density modulation of SPG,while this effect does not exist in OPG model;(2)SPG has much higher energy absorption rate from the infrared laser pulse;(3)Both SPG and OPG will have high ionization rate when neutral gases are added to the systems.