Generation,Acceleration And Applications Of Laguerre-Gaussian Laser Driven Ultrashort Electron Bunches

With the development of ultrafast physics,the motion of atoms and molecules in mat-ter is observed in real time on the femtosecond time scale.As the research progresses,it is expected to observe and control the internal state of atoms on the attosecond time scale.High-quality ultrashort electron pulses promote the continuous advancement of ultrafast technology.Although traditional accelerators can accelerate electrons to extremely high energy,it is difficult to generate ultrashort electron pulses with duration of below 100 fs due to the limitations of injector technology and bunch stretching effects.With the continuous advancement of laser technology,especially the Q-switching technology,laser mode-locking technology and chirped pulse amplification technology,the duration of the laser pulses is compressed from nanoseconds(10^-9s)to femtoseconds(10^-15s),and peak power has also been increased from megawatts?10⁶W?to petawatt(10¹⁵W).At present,the peak intensity of the laser pulse has exceeded 10²²W/cm².Therefore,the ultrashort ultraintense laser pulse interaction with matter has an inherent advantage in the generation of ultrashort electron pulses.The generation of ultrashort ultraintense laser pulses also pushes the laser-matter interaction to the relativistic regime where the relativistic electron dynamics in the laser fields become dominant.Optical processes driven by relativistic particle motion in plasmas,so-called“relativistic plasma optics”,facilitate investigation of ultrafast physics phenomena and the development of compact radiation sources.The short energetic electron beam has significant potential for applications such as electron diffraction and microscopy,four-dimensional?4D?electron imaging,and electron injection into a free electron laser?FEL?.Especially,this leads to the production of ultrashort x-ray radiation sources with duration down to the attosecond level.In these fields,femtosecond and even attosecond relativistic electron bunches with a narrow energy spread,small divergence angle and large flux are of crucial importance.For this purpose,significant efforts have been dedicated to acquiring high-quality ultrashort electron pulses.Due to the outward transverse ponderomotive force of the Gaussian laser pulse and Coulomb repulsion force,the produced electron pulse disperses quickly along the transverse direction.The generated attosecond electron pulses with a short duration?<50 fs?,a large emission angle?>20??and a low density?much less than the electron critical density?,can't be widely applied in various fields.Currently,it's still a great challenge to generate high-quality attosecond electron pulses.In order to overcome these difficulities that have plagued people for many years,we propose a novel scheme to generate high-quality ultrashort electron pulses via the interaction of the Laguerre-Gaussian laser pulse and microstructure target through theoretical analysis and numerical simulation.The main structure of the dissertation is as follows:Firstly,we systematically investigate the nonlinear dynamics of a single electron in the ultraintense Laguerre-Gaussian laser field.It is found that the single electron os-cillates violently in the linearly-polarized Laguerre-Gaussian laser fields and gradually moves away from the center of the laser field,due to unbalanced force in the transverse direction.Then the longitudinal and transverse electric field components of the laser pulse compete with each other in the electron acceleration,and the final energy of the electron is close to 100 MeV.In the left-handed circularly-polarized Laguerre-Gaussian laser fields,the single electron keeps in balance in the lateral direction and is constrained to the vicin-ity of the laser optical axis.Due to the negative laser longitudinal electric field?E_x<0?,the dephasing rate R of the electron is reduced to close to zero,and the electron is phase-locked in the longitudinal direction.It is also found that the laser longitudinal electric field dominates the electron acceleration.The angular momentum of the laser pulse is effec-tively transferred to the electron.In a right-handed circularly-polarized Laguerre-Gauss laser field,the electron drifts outward along the y and z directions due to the unbalanced lateral force.The transverse component of the laser electric field dominates the electron acceleration.This work provides a solid theoretical foundation and a strong holder for the thorough study in the interaction of ultraintense Laguerre-Gaussian laser pulse and nanowires or droplets.Secondly,we investigate the dynamics of ultraintense Laguerre-Gaussian laser puls-es interacting with a microwire target across-the-board and propose a novel physical scheme for the generation of high-quality attosecond electron bunch.When a relativistic LG-mode laser pulse sweeps a microwire target,annular electron bunches with attosec-ond duration are periodically dragged out of the left tip of the slice.Due to the radial laser electric field force exerted on the electrons,the annular bunches are tightly constrained near the target surface and steadily propagate along the microwire.A strong return current is thus induced and the resulant azimuthal magnetic fields pinch the charged particles in the target tightly.Once leaving from the right tip of the target,the electron emission angle gradually decreases and each hollow electron bunch is converged into an electron disc.Under the action of the longitudinal electric field,electrons are continuously accelerated to100s MeV.At the same time,the laser angular momentum is transferred efficiently to the beam angular momentum?BAM?of the bunches.The structure of the dense short electron bunches is stable and keeps intact for more than 300 femtoseconds.We can manipulate the quality of the bunches by changing the laser and target parameters,such as the laser handedness and intensity,beam waist radius,microwire length and radius.The scheme paves the way for the generation of high-quality attosecond electron bunches with low divergence,high beam charge and large BAM,which may have wide-range applications in various domains.Thirdly,we thoroughly investigate dense relativistic electron mirror generation from a micro-droplet driven by circularly-polarized Laguerre-Gaussian lasers.The surface electrons are expelled from the droplet by the laser radial electric field and evolve into dense sheets after leaving the droplet.These electrons are trapped in the potential well of the laser transverse ponderomotive force and are steadily accelerated to more than 100MeV by the inherent longitudinal electric field.Particle-in-cell simulations indicate that the relativistic electron mirrors are characterized by high beam charge,narrow energy spread and large angular-momentum.The scheme reduces requirements for the laser in-tensity and aiming accuracy,and improves the feasibility in experiments,which thus lays a foundation for the application of generated relativistic electron mirrors for bright com-pact X/?-ray pulse generation and photon vortex formation.Fourthly,we innovatively propose to generate an isolated attosecond pulse via a few-cycle circularly-polarized Laguerre-Gaussian laser pulse.It has been found that by rea-sonably changing the carrier-envelope phase and the laser intensity,the phase-locked po-sition of the ultrashort electron pulse in the Laguerre-Gauss laser field can be controlled.When the carrier-envelope phase?₀???,3?/2?,a stable quasi-monoenergetic isolated attosecond electron pulse can be generated.When a high-density carbon target is seated behind the droplet,the driven laser pulse can be reflected.An isolated attosecond?ray pulse with a duration of 300 as(10^-18s)and a maximum photon energy of 45 MeV can be generated via the nonlinear Compton scattering.The generated isolated attosecond pulse via this scheme may be widely applied in various fields of attosecond physics,such as at-tosecond photoelectron spectroscopy,4D imaging of electrons with subatomic resolution in space and time,and steering electrons with the electric field of synthesized light.