Electron Acceleration In Vacuum Research Articles

Laser induced electron acceleration in vacuum

Electron acceleration by a plane polarized laser wave has been studied in vacuum. Relativistic equations of motion have been solved exactly for electron trajectory and energy as a function of laser intensity, phase θ of the laser wave and initial electron energy. The electric field of the laser wave is taken as E=x̂A0 cos(ωt−kz+θ). Electron energy is maximum when θ=π/2 and (ωt−kz)=(2n−1)π, where n=1,2,3,… . The peak electron energy increases with laser intensity and initial electron energy. If a propagating laser pulse is abruptly stopped by a thin foil, the highly energetic electrons will continue to move forward inertially and escape from the pulse, as well as the thin foil, without much loss in the energy, if their stopping distance is much larger than the laser skin depth and the thin foil thickness, respectively.

Efficient acceleration of electrons with counterpropagating intense laser pulses in vacuum and underdense plasma.

We propose that efficient acceleration of electrons in vacuum and underdense plasmas by an intense laser pulse can be triggered in the presence of another counterpropagating or intersecting laser pulse. This mechanism works when the laser fields exceed some threshold amplitudes for stochastic motion of electrons, as found in single-electron dynamics. Particle-in-cell simulations confirm that electron heating and acceleration in the case with two counterpropagating laser pulses can be much more efficient than with one laser pulse only. Two different diagnoses show that the increased heating and acceleration are caused mainly by direct laser acceleration rather than by plasma waves. In plasma at moderate densities such as a few percent of the critical density and when the underdense plasma region is large enough, the Raman backscattered and side-scattered waves can grow to a sufficiently high level to serve as the second counterpropagating or intersecting pulse and trigger the electron stochastic motion. As a result, even with a single intense laser pulse only in plasma, electrons can be accelerated to an energy level much higher than the corresponding laser ponderomotive potential.

Accurate description of Gaussian laser beams and electron dynamics

Abstract In this paper, the higher order corrections to the description of a Gaussian laser field are derived and expressed as power functions of the parameter s=1/kw0, where k is the laser wave number and w0 the beam width at the focus center. Using the test particle simulation programs, the electron dynamics obtained using the paraxial approximation, the fifth-order correction, and the seventh-order correction are compared. Special attention is given to electron acceleration in vacuum by intense laser beams. The results reveal that, when kw0≳50, the paraxial approximation field is good enough to reproduce all the electron dynamic characteristics. In the range of 40≲kw0

Reply to “Comment On ‘Vacuum electron acceleration by coherent dipole radiation’ ”

Wang et al. [Phys. Rev. E 65, 028501 (2002)] claim that an electron interacting in vacuum with a unipolar plane electromagnetic wave will permanently gain energy, thus circumventing the Lawson-Woodward Theorem. We demonstrate that realistic, three-dimensional unipolar impulses cannot permanently impart energy to electrons in vacuum, leaving only the idealistic, one-dimensional, plane-wave impulse as a topic for academic discussion. We also note in passing that the version of the Lawson-Woodward theorem, which they are employing, is an erroneous version that has emerged in the laser acceleration literature over the last decade, and we direct the reader to the relevant papers containing the correct version of the theorem. Finally, we show that both our work and the proposal of Wang et al. are consistent with the correct version of this theory, and that the criticism by Wang et al. is thus without merit.

Characteristics of laser-driven electron acceleration in vacuum

The interaction of free electrons with intense laser beams in vacuum is studied using a three-dimensional test particle simulation model that solves the relativistic Newton–Lorentz equations of motion in analytically specified laser fields. Recently, a group of solutions was found for very intense laser fields that show interesting and unusual characteristics. In particular, it was found that an electron can be captured within the high-intensity laser region, rather than expelled from it, and the captured electron can be accelerated to GeV energies with acceleration gradients on the order of tens of GeV/cm. This phenomenon is termed the capture and acceleration scenario (CAS) and is studied in detail in this article. The accelerated GeV electron bunch is a macropulse, with duration equal to or less than that of the laser pulse, which is composed of many micropulses that are periodic at the laser frequency. The energy spectrum of the CAS electron bunch is presented. The dependence of the energy exchange in the CAS on various parameters, e.g., a0 (laser intensity), w0 (laser radius at focus), τ (laser pulse duration), b0 (the impact parameter), and θi (the injection angle with respect to the laser propagation direction), are explored in detail. A comparison with diverse theoretical models is also presented, including a classical model based on phase velocities and a quantum model based on nonlinear Compton scattering.

Vacuum electron acceleration by an intense laser

Using three dimensional test particle simulations, the characteristics and essential conditions under which an electron, in a vacuum laser beam, can undergo a capture and acceleration scenario (CAS) have been examined. When a0≳100 the electron can be captured and violently accelerated to energies ≳1 GeV, with an acceleration gradient ≳10 GeV/cm, where a0=eE0/meωc is the normalized laser field amplitude. The physical mechanism behind the CAS is that diffraction of the focused laser beam leads to a slowing down of the effective wave phase velocity along the captured electron trajectory, such that the electron can be trapped in the acceleration phase of the wave for a longer time and thus gain significant energy from the field.

High-intensity laser-induced electron acceleration in vacuum.

In this paper, an approximate pulsed-laser-beam solution of Maxwell's equation in vacuum is derived. Then with the numerical simulation method, electron acceleration induced by high-intensity [Q(0)=eE(0)/(m(e)omega c)=3] lasers is discussed in connection with the recent experiment of Malka et al. It is found that the maximum energy gain and the relationship between the final energy and the scattering angle can be well reproduced, but the polarization effect of electron-laser interactions is not very prominent. These results show that the ponderomotive potential model is still applicable, which means that the stimulated Compton scattering is the main fundamental mechanism responsible for the electron acceleration at this laser intensity.

Vacuum electron acceleration by coherent dipole radiation.

The validity of the concept of laser-driven vacuum acceleration has been questioned, based on an extrapolation of the well-known Lawson-Woodward theorem, which stipulates that plane electromagnetic waves cannot accelerate charged particles in vacuum. To formally demonstrate that electrons can indeed be accelerated in vacuum by focusing or diffracting electromagnetic waves, the interaction between a point charge and coherent dipole radiation is studied in detail. The corresponding four-potential exactly satisfies both Maxwell's equations and the Lorentz gauge condition everywhere, and is analytically tractable. It is found that in the far-field region, where the field distribution closely approximates that of a plane wave, we recover the Lawson-Woodward result, while net acceleration is obtained in the near-field region. The scaling of the energy gain with wave-front curvature and wave amplitude is studied systematically.

Vacuum laser acceleration by an ultrashort, high-intensity laser pulse with a sharp rising edge

A laser vacuum electron acceleration scheme is proposed in this letter. By the help of a one-dimensional model, we find that an ultrashort, high-intensity, plane-wave laser pulse with a sharp rising edge can be used to accelerate electrons to relativistic energy in vacuum.

Laser driven electron acceleration in vacuum, gases, and plasmas

In this paper we discuss some of the important issues pertaining to laser acceleration in vacuum, neutral gases, and plasmas. The limitations of laser vacuum acceleration as they relate to electron slippage, laser diffraction, material damage, and electron aperture effects, are discussed. An inverse Cherenkov laser acceleration configuration is presented in which a laser beam is self-guided in a partially ionized gas. Optical self-guiding is the result of a balance between the nonlinear self-focusing properties of neutral gases and the diffraction effects of ionization. The stability of self-guided beams is analyzed and discussed. In addition, aspects of the laser wakefield accelerator are presented and laser-driven accelerator experiments are briefly discussed.

Vacuum laser acceleration

Abstract : The purpose of this communication is to comment on and discuss laser acceleration of electrons in vacuum. In particular, we will: (1) critique the recent paper by C. M. Haaland, titled Laser Electron Acceleration in Vacuum, (2) discuss some general features and characteristics of laser acceleration in vacuum, and (3) propose a laser acceleration concept called the vacuum beat wave accelerator.

Response to comments on laser electron acceleration in vacuum

Response is made to criticisms on Haaland's paper on acceleration of electrons by laser beams in vacuum. All claims by critics are refuted.

Laser acceleration of electrons in vacuum.

Several features of vacuum laser acceleration are reviewed, analyzed, and discussed, including electron acceleration by two crossed laser beams and acceleration by a higher-order Gaussian beam. In addition, the vacuum beat wave accelerator (VBWA) concept is proposed and analyzed. It is shown that acceleration by two crossed beams is correctly described by the Lawson-Woodward (LW) theorem, i.e., no net energy gain results for a relativistic electron interacting with the laser fields over an infinite interaction distance. Finite net energy gains can be obtained by placing optical components near the laser focus to limit the interaction region. The specific case of a higher-order Gaussian beam reflected by a mirror placed near focus is analyzed in detail. It is shown that the damage threshold of the mirror is severely limiting, i.e., substantial energy gains require very high electron injection energies. The VBWA, which uses two copropagating laser beams of different frequencies, relies on nonlinear ponderomotive forces, thus violating the assumptions of the LW theorem. Single-particle simulations confirm that substantial energy gains are possible and that optical components are not needed near the focal region.

Laser electron acceleration in vacuum

This scheme involves pairs of intersecting linearly-polarized Gaussian-profile laser beams that are focused at crossover in vacuum and phased such that transverse field components cancel. The E z components accelerate properly-phased z-axis relativistic electrons throughout a half-wave slip distance centered at crossover. The slip length is approximately 90λ for the case considered. The E z components vanish rapidly before and after this slip region, thus providing conditions for a special case that is not included in Palmer's general acceleration theorem. Electron energy-gain gradients of several GeV/m appear to be possible.

Acceleration of electrons in vacuum by two laser beams

A method of acceleration is proposed in which electrons gain energy at the intersection of two laser beams. The interaction takes place in vacuum far away from any conductor or dielectric, avoiding the usual breakdown problems. An acceleration gradient of more than 1 GeV/m is produced for a CO2 laser of 1014 W/cm2.