Laser Beam In Vacuum Research Articles

Efficient electron acceleration by using Hermite-cosh-Gaussian laser beam in vacuum

The electron acceleration in vacuum has been studied theoretically using a radially polarized (RP) Hermite-cosh-Gaussian (HChG) laser beam. Even if the laser’s power is low, the RP HChG laser beam is quite effective and responsible for producing high energy electron. Due to the beauty (earlier focus) of such a laser beam, it is significantly better suited to acquiring GeV order energy over short periods of time than other laser beams. The electron acceleration process is strongly influenced by two more adjustable parameters associated with this beam: decentered parameter (b) and Hermite order (s). Throughout this investigation, better trapping phenomena have been identified. The effects of changing the intensity parameter (), the beam waist width (), the decentered parameter (b), and the order of the Hermite function on electron energy gain have been investigated.

Electron acceleration from transparent targets irradiated by ultra-intense helical laser beams

The concept of electron acceleration by a laser beam in vacuum is attractive due to its seeming simplicity, but its implementation has been elusive, as it requires efficient electron injection into the beam and a mechanism for counteracting transverse expulsion. Electron injection during laser reflection off a plasma mirror is a promising mechanism, but it is sensitive to the plasma density gradient that is hard to control. We get around this sensitivity by utilizing volumetric injection that takes place when a helical laser beam traverses a low-density target. The electron retention is achieved by choosing the helicity, such that the transverse field profiles are hollow while the longitudinal fields are peaked on central axis. We demonstrate using three-dimensional simulations that a 3 PW helical laser can generate a 50 pC low-divergence electron beam with a maximum energy of 1.5 GeV. The unique features of the beam are short acceleration distance (∼100 μm), compact transverse size, high areal density, and electron bunching (∼100 as bunch duration).

Electron Acceleration by a radially polarised cosh-Gaussian laser beam in vacuum

In this paper, a radially polarised cosh-Gaussian laser beam (CGLB) is used to study the electron acceleration produced in vacuum. A highly energetic electron beam can be achieved by a CGLB, even with comparatively low-powered lasers. The properties of a CGLB cause it to focus earlier, over a shorter duration than a Gaussian laser beam, which makes it suitable for obtaining high energies over small durations. It is found that the energy gained by the electrons strongly depends upon the decentering parameter of the laser profile. It is also observed that for a fixed value of energy gain, if the decentering parameter is increased, then the intensity of the laser field decreases. The dependence of the energy gained by electrons on the laser intensity and the laser-spot size is also studied.

Linear and nonlinear propagation characteristics of multi-Gaussian laser beams

Theoretical investigation on the propagation characteristics of a new class of laser beams known as multi Gaussian (M.G) laser beams has been presented. To investigate the linear characteristics, propagation of the laser beam in vacuum has been considered. Whereas, the nonlinear characteristics have been investigated in plasmas. Optical nonlinearity of the plasma has been modeled by relativistic mass nonlinearity of the plasma electrons in the field of laser beam. Formulation is based on finding the semi analytical solution of the wave equation for the slowly varying envelope of the laser beam. Particularly, the dynamical evolutions of the beam width and longitudinal phase of the laser beam have been investigated in detail.

Benefits And Prospects Of Laser Welding Application In Vacuum

<p>In the recent years laser beam welding has been more and more broadly used in the industry for the production of details of significant appointment. One of the perspective directions of laser technologies for the production of significant products of big thickness is the welding by the concentrated laser beam in vacuum that allows producing faultless welded seams with the high relation of seam depth to its width. The conducted researches confirm results of theoretical modeling of processes at laser beam welding.</p>

Welding with the Laser Beam in Vacuum

AbstractIn the vehicle industry, beam welding methods are successfully applied for the joining of high‐quality parts. Here, the focus is mainly put on drive section components. Especially in component manufacturing of couplings, toothed wheel — shaft joints and drive shafts, electron beam welding using small vacuum cycle chambers is applied. The application of powerful solid‐state lasers results, however, often in negative consequences, such as soiling by process emissions or increased tendency to spatter. The application of laser beam welding in vacuum allows for the reduction of these side effects and, at the same time, for the increase of penetration depth and weld quality. This article introduces first results gained from tests made with workpieces from the vehicle industry.

Self-induced mode mixing of ultraintense lasers in vacuum

We study the effects of the quantum vacuum on the propagation of a Gaussian laser beam in vacuum. By means of a double perturbative expansion in paraxiality and quantum vacuum terms, we provide analytical expressions for the self-induced transverse mode mixing, rotation of polarization, and third harmonic generarion. We discuss the possibility of searching for the self-induced, spatially dependent phase shift of a multipetawatt laser pulse, which may allow the testing of quantum electrodynamics and new physics models, such as Born-Infeld theory and models involving new minicharged or axion-like particles, in parametric regions that have not yet been explored in laboratory experiments.

Influence of the intensity gradient upon HHG from free electrons scattered by an intense laser beam

When an electron is scattered by a tightly-focused laser beam in vacuum, the intensity gradient is a critical factor to influence the electron dynamics, for example, the electron energy exchange with the laser fields as have been explored before [P.X.Wang et al.,J. Appl. Phys. 91, 856 (2002]. In this paper, we have further investigated its influence upon the electron high-harmonic generation (HHG) by treating the spacial gradient of the laser intensity as a ponderomotive potential. Based upon perturbative QED calculations, it has been found that the main effect of the intensity gradient is the broadening of the originally line HHG spectra. A one-to-one relationship can be built between the beam width and the corresponding line width. Hence this finding may provides us a promising way to measure the beam width of intense lasers in experiments. In addition, for a laser pulse, we have also studied the different influences from transverse and longitudinal intensity gradients upon HHG.

Quantum interaction among intense laser beams in vacuum

Quantum electrodynamics (QED) predicts that electromagnetic fields interact among each other also in vacuum. We study the possibility of experimentally revealing this interaction by using soon available laser fields with intensities of order of $10^{23}\text{--}10^{26}\,\text{W/cm$^2$}$ . First, a few processes are first reviewed where vacuum polarization effects can be detected, like laser-assisted photon-photon scattering and the light diffraction by a strong standing wave. The possibility of enhancing these effects by using a plasma is also mentioned. Finally, the process of photon splitting in a laser field is discussed in detail together with its possible experimental observation.

Direct acceleration of electrons by intense crossed Hermite–Gaussian laser beams

Abstract Electron acceleration by two crossed linearly polarized Hermite–Gaussian laser beams in vacuum has been proposed and investigated in the Letter. The laser fields have the same amplitude and frequency. To accelerate electrons along z -axis directly, the necessary conditions and energy gain expressions are given.

Direct acceleration of electrons by a Laguerre-Gaussian laser beam in vacuum

The acceleration of electrons by a Laguerre-Gaussian(LG) beam in vacuum is studied. It is shown that only the longitudinal electric field of the LG beam with mode indices p and l=1 can be used to accelerate electrons. The linearly- and circularly-polarized LG beams with mode indices p and l=1 effectively play the role in laser electron acceleration. Some physical characteristics, such as phase and group velocities of the axial optical field, and energy gain of electrons etc., are discussed. The analytical expressions for the phase and group velocities of the axial optical field, accelerating potential and energy gain etc. are derived and are used to make numerical analysis.

Optimal injection scheme for electron acceleration by a tightly focused laser beam

Electron dynamics and energy gain in a tightly focused laser beam in vacuum are investigated by numerical simulations. There exist two acceleration mechanisms, i.e. acceleration by the longitudinal field or by the transverse field, which corresponds to two different trajectories. The relationship between the energy gain and the injection parameters of electrons, including the injection angle and momentum, is shown. For given laser parameters, the optimum injection parameters can be obtained.

Energy-angle correlation of electrons accelerated by laser beam in vacuum

The correlation between the outgoing energy and the scattering angle of electrons accelerated by a laser beam in vacuum has been investigated. Essentially, the single-valued function of the correlation, derived from classical electrodynamics Compton scattering for a plane wave, is broadened to a band. It means electrons with the same outgoing energy will have an angular spread. An equation to describe this correlation has been derived. Dependence of the spread width of scattering angle on laser beam parameters is examined, and physical explanations of these features are given. The results are found to be consistent with the simulation results for a proposed vacuum laser acceleration scheme: the capture and acceleration scenario.

Characteristics of multimode combined intense laser-induced electron acceleration and violent bunch compression

The interaction of low energy electrons with multimode combined intense laser beams in vacuum was studied by using three-dimensional test particle simulation. The process of interaction and the ponderomotive potential structures of some multimode combined intense laser beams are analyzed in detail. This article presents the detailed characteristics of the multimode combined intense laser-induced electron acceleration and violent bunch compression [Wang et al., Appl. Phys. Lett. 82, 2752 (2003)]. The properties of the output electron bunch are also investigated.

Electron acceleration by a tightly focused femtosecond laser beam in vacuum

Ponderomotive-force driven acceleration of an electron at the focus of a high-intensity short-pulse laser is considered using a model that the electrons accelerated are near the focus but decelerated far away the focus. For intensities above 1019Wμm2/cm2, the electron's energy gain in the range of MeV can be realized when the electron leaves the laser pulse. Final energy gain of the electron as a function of its initial position has also been discussed. We find that an electron initially near the focus can be accelerated well.

Multimode combined intense laser-induced electron acceleration and violent bunch compression

The ponderomotive potential structure of a multimode combined intense laser beam is studied. Using a three-dimensional test particle simulation, the interaction of slow electrons with the combined laser beam in vacuum is investigated. The calculation shows that electrons distributed on a large scale can be accelerated to relativistic energy in vacuum. A violent longitudinal bunch compression phenomenon is also presented and discussed.

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.

Effects of O, H and N passivation on photoluminescence from porous silicon

A simple but effective passivation method for porous silicon (PS) has been developed. Immersion of as-etched PS in dilute (NH 4) 2S/C 2H 5OH solution followed by ultraviolet light irradiation in air can lead to an enhancement of photoluminescence (PL) up to more than 20 times. Infrared absorption and Auger electron spectroscopic measurements show that the formation of SiH(O 3), SiOSi and SiN bonds are formed during the post-treatment process. However, the PL intensity cannot be enhanced if the solution-treated sample is exposed to the laser beam in vacuum. It is thus concluded, that the PL enhancement can be attributed to the presence of compact passivation films consisting of the oxides and the nitride on both external and internal surfaces of the sponge-like PS samples.

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.

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.