Field Structure And Electron Acceleration In A Laser Beam Of High-order Laguerre-Gaussian Mode

With the development of laser technology and the increasing desire for efficient and cheap high-energy particle accelerators,the schemes of laser-driven charged particles have received great attention.Though the scenario of laser/plasma acceleration has been made some breakthroughs in experiment,some disadvantages with laser/plasma acceleration such as Gas Breakdown,Medium Damage and Plasma Instability can be avoided in vacuum acceleration schemes.Up to now,many vacuum laser-driven schemes have been proposed,their mechanisms can be classified into two main kinds:Ponderomotive Acceleration for low-energy injection electrons and Capture Acceleration for high-energy injection electrons.For a fundamental mode Gaussian laser beam,whose radial intensity distribution is Gaussian shape,the paraxial injected electrons will be quickly ejected from the strong field area because of the radial ponderomotive force,and then the electrons can not be well accelerated by the axial ponderomotive force.Capture acceleration is viable owe to the high-intensity longitudinal electric field distribution as well as the low wave phase velocity distribution.For the Fundamental mode Gaussian beam,the transversal electrical intensity in the central area is very high but longitudinal electrical intensity is almost zero,and where the phase velocity is far higher than light velocity.In other words, the so-called high-intensity area is not helpful for capture acceleration. Therefore,scientists suggest acceleration with the high-order Gaussian mode laser beam.In principle,the high-order Gaussian mode laser beam could provide higher-intensity longitudinal electrical field,which is helpful for capture acceleration.Furthermore,compared with the Fundamental mode Gaussian laser beam,the high-order Gaussian mode laser beam has a flatter paraxial electrical intensity distribution, accordingly the abaxial transversal Ponderomotive force reduces greatly, which may be helpful for Ponderomotive acceleration.Many research works about the high-order Hermite-Gaussian mode laser beam for acceleration have been put forward,but little with the high-order Laguerre-Gaussian(LG) mode.In this paper,we first analyze the field intensity distribution of the high-order LG mode laser beam,especially study the electrical field intensity distribution and the phase velocity distribution of two typical high order modes(ρ=4,e=0 andρ=4,e=1,ρis the radial index and e the azimuthal mode index.For convenience,we cite as LG40 and LG41) in details.Numerical results of the electron acceleration process in LG40 and LG41 mode laser beam are present and compared with that in the fundamental mode(LG00) laser beam.We found that the high-order LG mode laser beam displays obvious advantages for low energy injection electrons,especially in the sameρand e＞0 cases. Contrary to people's expectations,the acceleration effect of a high-order LG mode laser beam for high energy incident electrons is not as good as the LG00 mode,even if high order mode laser beam has a high longitudinal intensity electrical field distribution.Associated with the poderomotive acceleration and capture acceleration models,our simulative results are analyzed.