Study On The Generation Of Femtosecond Magnetic Pulses By Circularly Polarized Vortex Laser Driven Plasma

The study of pulsed magnetic fields dates back to the early 20 th century.Ultrashort pulsed magnetic fields allow for a better understanding of ultra-fast physical microprocesses,including domain wall motion and spin-orbit interactions,which occur within time scales ranging from microseconds to femtoseconds.Femtosecond magnetic field pulses are particularly valuable for studying ultra-fast magnetization,demagnetization,magnetic storage,and spin ultra-fast dynamics.Traditional pulsed magnetic fields are limited by the performance of the pulse power source and are incapable of producing ultra-short pulsed magnetic fields below the millisecond level.As a result,it is not possible to study magnetic dynamics at the femtosecond scale using this method alone.Currently,using ultra-short pulsed laser-driven electron streams is an effective way of generating femtosecond magnetic field pulses.This paper aims to establish a three-dimensional model of the interaction between the driving optical field and the plasma target.The model will simulate physical processes such as light propagation,free electron movement,vortex current,and pulsed magnetic field generation,and will optimize relevant parameters to produce femtosecond magnetic field pulses.Research has shown that ultra-short pulse lasers generate hot electrons on the surface of plasma targets.These electrons pass through the target material and become excited,leading to strong charge separation on the back surface.This,in turn,causes these electrons to accelerate and produce powerful electromagnetic radiation under the laser’s influence.The PIC method is an essential simulation tool used for a range of applications,from laboratory experiments to astrophysics.It relies on the kinetic theory and electromagnetic theory of plasma and solves the Vlasov-Maxwell equations to model the evolution of particle distribution functions over time.This article employs the physical mechanism of plasma surface-sheath oscillation and utilizes the PIC method and Smilei program to simulate the Tesla-level femtosecond magnetic field pulse generated by the interaction between circularly polarized Laguerre-Gaussian beams and low-density plasma.The principal focus and unique features of this article are outlined below.(1)Using the PIC method and Smilei program,we simulated the propagation of Gaussian beams in vacuum under the paraxial approximation.We then compared the simulation results with theoretical calculations and found an error of about 4.5%,which fell within the allowable range.We also simulated the propagation of Laguerre Gaussian beams in vacuum and observed a consistent optical field distribution with theoretical calculations.In addition,we demonstrated the capability of the simulation to model the interaction between circularly polarized Gaussian beams and plasma,resulting in a spiral electron trajectory.To simulate physical processes like light propagation and free electron generation,we established a three-dimensional model to drive the optical field and plasma target interaction.(2)The electronic motion in a plasma driven by circularly polarized LaguerreGaussian beams was simulated using the PIC method and Smilei program.This simulation resulted in the generation of photocurrent and femtosecond magnetic field pulses.The study aimed to investigate the effects of laser intensity,waist radius,and plasma density on the magnetic pulses.The results show that ultra-short magnetic pulses with peak intensities ranging from 0.5 to 50 T and pulse widths of approximately 10 fs can be generated.The pulse width of the magnetic field is consistent with that of the driving light,and its intensity increases with the increase of laser intensity,waist radius,and plasma density.The study provides systematic insights into the generation of magnetic pulses in plasmas driven by circularly polarized Laguerre-Gaussian beams.The simulation above generated femtosecond magnetic pulses and optimized their generation by adjusting various parameters.This article not only utilizes the interaction between ultra-short pulse lasers and plasmas to generate femtosecond magnetic field pulses,but also investigates variations in pulse magnetic field intensity based on different laser parameters and plasma density conditions.The aim of this study is to discover the optimal experimental parameters for creating femtosecond magnetic field pulses,ultimately taking ultrafast magnetodynamics research to the next level in terms of the femtosecond timescale.