Vacuum Laser Acceleration Research Articles

Subluminous phase velocity of a focused laser beam and vacuum laser acceleration.

It has been found that for a focused laser beam propagating in free space, there exists, surrounding the laser beam axis, a subluminous wave phase velocity region. Relativistic electrons injected into this region can be trapped in the acceleration phase and remain in phase with the laser field for sufficiently long times, thereby receiving considerable energy from the field. Optics placed near the laser focus are not necessary, thus allowing high intensities and large energy gains. Important features of this process are examined via test particle simulations. The resulting energy gains are in agreement with theoretical estimates based on acceleration by the axial laser field.

Output features of vacuum laser acceleration

Electrons acceleration by the vacuum laser acceleration scheme CAS [see, e.g., P. X. Wang et al., Appl. Phys. Lett. 78, 2253 (2001)] (capture and acceleration scenario) is simulated. The general features of the outgoing electrons are examined at different laser intensities. Explanations based on the mechanism behind the CAS scheme of those output characteristics are presented. The results show it is hopeful that CAS becomes a useful scheme for laser accelerators.

Electron dynamics characteristics in high-intensity laser fields

This paper addresses the conditions under which the vacuum laser acceleration scheme CAS (capture and acceleration scenario), newly proposed by the authors (see, e.g., P.X. Wang et al., Appl. Phys. Lett. 78, 2253 (2001)), can be observed. Specifically, the laser intensity threshold (a0)th and the range of the electron incident momentum for the CAS scheme to emerge are examined. We found that (a0)th is critically dependent on the laser beam width w0. At kw0=60, (a0)th=8, which is an intensity obtainable using present laser systems. The required energy of the incident electron is in the range 5–15 MeV. This study is of significance in designing an experimental setup to test CAS and helpful in understanding the basic physics of CAS.

Ponderomotive laser acceleration and focusing in vacuum for generation of attosecond electron bunches.

A novel approach for the generation of ultrabright attosecond electron bunches is proposed, based on acceleration in vacuum, by a short laser pulse. The laser-pulse profile is tailored such that the electrons are both focused and accelerated by the ponderomotive force of the light. Using time-averaged equations of motion, analytical criteria for optimal regime of acceleration are found. It is shown that for realistic laser parameters, a beam with up to 10(6) particles and normalized transverse and longitudinal emittances <10(-8) m can be produced.

Generation of Sub-picosecond GeV Electron Bunches by Laser Acceleration in Vacuum

The interaction of free electrons with intense laser beams in vacuum was studied using 3D test particle simulation instead of analytically solving the relativistic Newton-Lorentz equation of motions. We found a group of solutions for the equation, which reveal very interesting and unusual characteristics different from any previously reported. The fundamental characteristics of those trajectories are that an electron can be captured into the high-intensity region, rather than expelled from it and that the captured electron can be accelerated to GeV energy with an acceleration gradient of 1–50 GeV/cm. These solutions emerges only when the laser intensity is a0\\gtrsim100, where a0≡eE0/meωc is a measure of the laser intensity. The accelerated GeV electron bunch is a macropulse composed of multiple micropulses, which is analogous to the structure of bunches produced by conventional linacs. The paraxial approximation equations for the Gaussian laser beam used in the simulation are highly accurate and the contribution of the high-order correction is almost negligible when the laser beam width is w0\\geqslant60.

Review of some selected experiments on laser electron–beam interaction

The third-generation 1.5 GeV electron storage ring DELTA, dedicated to synchrotron-radiation experiments, accelerator technology and UV FEL operation, was commissioned about 2 years ago at the Dortmund University. After the first successful lasing in the visible region (470 nm) beginning of this year, it is planned to obtain lasing also in the UV near 200 nm and then later to use the high average intracavity power and natural synchronization of electron and optical pulses to produce intense beams of high-energy γ-rays by Compton backscattering. Applying these γ-rays, a photo-fission experiment of importance for nuclear astrophysics is described. Since the time resolution of high-brightness synchrotron light sources is limited to more than 10 ps, it is envisioned to test a novel technique for generating sub-picosecond X-ray pulses based on the interaction of the electrons with a co-propagating beam of femtosecond photon pulses from an external TW-laser. This technique will be applied at DELTA by using its superconducting wiggler and a permanent-magnet undulator. Simulations show that a brilliance of 10 8 photons/(s mm 2 mrad 2 0.1% bandwidth) with pulse durations of the order of 100 fs can be achieved. Using the magnetic insertions of DELTA and an external TW-laser will further allow measurements for testing laser acceleration in the ultra-high vacuum of a storage ring and of radiation damping of the beam emittance on a fast time scale. First, results of laser-beam monitoring at the stretcher ring AmPS to determine the transverse beam emittance are presented and are intended to be performed also at DELTA. For these investigations the electron beam has been scanned at 90° with a high-power laser beam, and forward-scattered Compton photons were detected to derive the beam profile.

Nonlinear Thomson scattering of two electromagnetic waves on the relativistic electron

The characteristics of Thomson scattering radiation of two weak electromagnetic (EM) waves forming a standing wave are calculated. It is shown that the effective mass of the electron in the field of the two EM-waves can be measured experimentally; the radiation can be used for microbunch diagnostics; the existence of a new type of radiation is predicted. The two EM-wave mechanism of vacuum laser acceleration of electrons is proposed, parameters of both waves (the first one is accelerating and the second ejecting the electron from the laser focus) are estimated and the limits of applicability are presented.

Principle of high accuracy for the nonlinear theory of the acceleration of electrons in a vacuum by lasers at relativistic intensities

Acceleration of electrons by lasers in a vacuum was considered impossible based on the fact that plane-wave and phase symmetric wave packets cannot transfer energy to electrons apart from Thomson or Compton scattering or the Kapitza–Dirac effect. The nonlinear nature of the electrodynamic forces of the fields to the electrons, expressed as nonlinear forces including ponderomotion or the Lorentz force, permits an energy transfer if the conditions of plane waves in favor of the beams and/or the phase symmetry are broken. The resulting electron acceleration by lasers in a vacuum is now well understood as “free wave acceleration”, as “ponderomotive scattering”, as “violent acceleration”, or as “vacuum beat wave acceleration”. The basic understanding of these phenomena relates to an accuracy principle of nonlinearity for explaining numerous discrepancies on the way to the mentioned achievement of “vacuum laser acceleration”, which goes beyond the well-known experience of necessary accuracy in both modeling and experimental work experiences among theorists and experimentalists in the field of nonlinearity. From mathematically designed beam conditions, an absolute maximum of electron energy per laser interaction has been established. It is shown here how numerical results strongly (both essentially and gradually) depend on the accuracy of the used laser fields for which examples are presented and finally tested by the criterion of the absolute maximum.

The chirped-pulse inverse free-electron laser: A high-gradient vacuum laser accelerator

The inverse free-electron laser (IFEL) interaction is studied theoretically and computationally in the case where the drive laser intensity approaches the relativistic regime, and the pulse duration is only a few optical cycles long. The IFEL concept has been demonstrated as a viable vacuum laser acceleration process; it is shown here that by using an ultrashort, ultrahigh-intensity drive laser pulse, the IFEL interaction bandwidth and accelerating gradient are increased considerably, thus yielding large energy gains. Using a chirped pulse and negative dispersion focusing optics allows one to take further advantage of the laser optical bandwidth and produce a chromatic line focus maximizing the gradient. The combination of these novel ideas results in a compact vacuum laser accelerator capable of accelerating picosecond electron bunches with a high gradient (GeV/m) and very low energy spread.

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.

Vacuum laser acceleration using a radially polarized CO 2 laser beam

Utilizing the high-power, radially polarized CO 2 laser and high-quality electron beam at the Brookhaven Accelerator Test Facility, a vacuum laser acceleration scheme is proposed. In this scheme, optics configuration is simple, a small focused beam spot size can be easily maintained, and optical damage becomes less important. At least 0.5 GeV/m acceleration gradient is achievable by 1 TW laser power.

ELECTRON DYNAMICS IN THE EXTRA-INTENSE STATIONARY LASER FIELD

Electron dynamics in the extra-intense stationary laser field has been investigated by numerical simulation method.It is found,for the first time to our knowledge,that when Q100(Q=eE/mecω,is a dimensionless parameter measuring the field intenstiy),the electron with relatively lower energy can be captured and violently accelerated by the laser beam.This is a new phenmenon which is of potential importance to the far-field laser acceleration in vacuum.

High-beam-quality electron acceleration in a vacuum by using two intersecting ultrashort, high-intensity laser pulses

The fact that electrons are accelerated by intense laser pulses in a vacuum is particularly apparent from recently published work, but up to now no high-beam-quality laser vacuum acceleration scheme has been presented. In this paper, numerical simulations demonstrate that free electrons can be accelerated axially (high beam quality) in a vacuum by using two intersecting ultrashort, high-intensity laser pulses. As the maximum intensities are on the laser axes, a hollow channel is formed between the two laser beams. The electrons will be expelled by the transverse ponderomotive force of each beam to the axis of the symmetry, and can be trapped inside the channel until they are accelerated to relativistic energies. This makes possible axial rather than radial acceleration.

Comment on “Experimental Observation of Electrons Accelerated in Vacuum to Relativistic Energies by a High-Intensity Laser”

The interpretation of the results of this paper werebased on electromagnetic fields that do not satisfyMaxwell’s equations and neglect the small but importantlongitudinal electric field near a focus. The intricatequestion of vacuum laser acceleration of free electronsdeserves more rigorous analysis.The experimental results presented by Malka et al. [1]address an issue that has been debated with vigor andcontroversy for decades: Under what conditions can afree electron extract energy from an electromagnetic fieldthat consists entirely of waves that obey the vacuumdispersion relation v ›

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.

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.