Electron Acceleration In Vacuum Research Articles

Investigating q-Gaussian laser pulse dynamics for enhanced electron acceleration in vacuum

Investigating q-Gaussian laser pulse dynamics for enhanced electron acceleration in vacuum

Unforeseen advantage of looser focusing in vacuum laser acceleration

Acceleration of electrons in vacuum directly by intense laser fields holds great promise for the generation of high-charge, ultrashort, relativistic electron bunches. While the energy gain is expected to be higher with tighter focusing, this does not account for the reduced acceleration range, which is limited by diffraction. Here, we present the results of an experimental investigation that exposed nanotips to relativistic few-cycle laser pulses. We demonstrate the vacuum laser acceleration of electron beams with 100s pC charge and 15 MeV energy. Two different focusing geometries, with normalized vector potential a0 of 9.8 and 3.8, produced comparable overall charge and electron spectra, despite a factor of almost ten difference in peak intensity. Our results are in good agreement with 3D particle-in-cell simulations, which indicate the importance of dephasing.

Chirped Cosh-Gaussian Electron Acceleration in Vacuum Due to Two Lasers

Chirped Cosh-Gaussian Electron Acceleration in Vacuum Due to Two Lasers

Radially Polarized Laser-Induced Electron Acceleration in Vacuum

Enhanced electron acceleration due to tightly focused (TF) short-intense radially polarized (RP) Gaussian laser pulse in vacuum has been investigated. An axicon optical lens is utilized to accomplish a TF laser beam. The TF-RP laser fields are truncated to fifth order in diffraction angle. The innate and attractive symmetry of the tightly focused RP laser pulse imposes the trapping of electrons in the route of the laser propagation throughout laser–electron interaction. The applied axial magnetic field further ensures the enhancement in ponderomotive strength, pushing the electron in the expediting phase up to longer distances. Utilizing the optimum parameters of RP laser and magnetic field, noteworthy augmentation in the electron acceleration up to GeV range is obtained. The electron energy gain variations are plotted and analyzed for initial laser intensity, initial phase, electron initial energy and applied magnetic field parameters.

Electron acceleration by higher-order cosh-gaussian laser pulses in vacuum

Higher-order Cosh-Gaussian (ch-G) laser pulse is proposed for effective electron acceleration and energy gain in vacuum. The intensity distribution of ch-G laser is influenced by its higher-order (m) and decentered parameter (b) controlled propagation features. The laser pulse order m= (0,1,2,3) classifies them as Gaussian, ch-G, ch-square-G, and ch-cube-G laser pulses. The flatter the beam profile becomes as the order (m) increases, with the loss of its initial maximum intensity center at a slower rate as m increases, making it suitable for long-distance propagation. The increase in decentered parameter b, changes its properties from Gaussian(b=0) to flat top (b>1) and ring-shaped (b∼2) forms. As a result, it operates well enough to quickly accelerate electrons to exceedingly high energies in a short period of time. The analytic results show that altering the m and b combination leads to a significant rise in electron energy with laser intensity (∼1020W/cm2) of the order of GeV in vacuum.

Revisiting Experimental Signatures of the Ponderomotive Force

The classical theory of single-electron dynamics in focused laser pulses is the foundation of both the relativistic ponderomotive force (RPF), which underlies models of laser-collective-plasma dynamics, and the discovery of novel strong-field radiation dynamics. Despite this bedrock importance, consensus eludes the community as to whether acceleration of single electrons in vacuum has been observed in experimental conditions. We analyze an early experiment on the RPF with respect to several features that were neglected in modeling and that can restore consistency between theory predictions and experimental data. The right or wrong pulse profile function, laser parameters, or initial electron distribution can each make or break the agreement between predictions and data. The laser phase at which the electron’s interaction with the pulse begins has a large effect, explaining why much larger energies are achieved by electrons liberated in the focal region by photoionization from high-Z atoms and by electrons ejected from a plasma mirror. Finally, we compute the difference in a typical electron spectrum arising from fluctuating focal spot size in state-of-the-art ultra-relativistic laser facilities. Our results emphasize the importance of thoroughly characterizing laser parameters in order to achieve quantitatively accurate predictions and the precision required for discovery science.

Retraction Note: Chirped laser beat wave electron acceleration in vacuum

Retraction Note: Chirped laser beat wave electron acceleration in vacuum

RETRACTED ARTICLE: Chirped laser beat wave electron acceleration in vacuum

RETRACTED ARTICLE: Chirped laser beat wave electron acceleration in vacuum

Investigation of electron acceleration in vacuum by a radially polarized laser pulse in the presence of helical wiggler field and axial magnetic field guiding

In this paper, electron acceleration by a radially polarized laser pulse in the presence of helical wiggler magnetic field and axial magnetic field has been studied. The governing equations on electron dynamics in the presence of these electric and magnetic fields were solved by the fourth order Runge-Kuta method. The effect of axial magnetic field and electron injection angle on energy gained by the electron was investigated. Numerical studies have shown that the final energy of an electron depends on the value of the magnetic field and the injection angle. It was seen that by applying a magnetic field of about 0.2 and the injection angle of about 11 degrees, the electron can gain final energy of about 3.8 GeV, which is 40 percent more than the case of zero degrees injection angle and the absence of external magnetic field.

Spatiotemporal modeling of direct acceleration with high-field terahertz pulses.

We present an improved model for electron acceleration in vacuum with high-energy THz pulses that includes spatiotemporal effects. In our calculations, we examined the acceleration with 300 GHz and 3.0 THz central frequency THz pulses with properties corresponding to common sources, and compared the Gaussian and Poisson spectral amplitudes and the associated time profiles of the electric fields. Our calculation takes into account both the longitudinal field and the spatio-spectral evolution around the focus. These aspects of the model are necessary due to the tight focusing and the duration towards a single-cycle of the THz pulses, respectively. The carrier-to-envelope phase (CEP) and the tilting angle of the coincident few- or single-cycle THz pulses must be tuned in all cases in order to optimize the acceleration scheme. We reveal additionally that electron beams with different final energies and different divergences can be generated based on simulated THz pulses having different Porras factors, describing the frequency dependence of the spatiotemporal amplitude profile, which may depend strongly on the method used to generate the single-cycle THz pulses.

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.

Enhanced coherent transition radiation from midinfrared-laser-driven microplasmas

We present a particle-in-cell (PIC) analysis of terahertz (THz) radiation by ultrafast plasma currents driven by relativistic-intensity laser pulses. We show that, while the I0{lambda }_{0}^{2} product of the laser intensity I0 and the laser wavelength λ0 plays the key role in the energy scaling of strong-field laser-plasma THz generation, the THz output energy, WTHz, does not follow the I0{lambda }_{0}^{2} scaling. Its behavior as a function of I0 and λ0 is instead much more complex. Our two- and three-dimensional PIC analysis shows that, for moderate, subrelativistic and weakly relativistic fields, WTHz(I0{lambda }_{0}^{2}) can be approximated as (I0λ02)α, with a suitable exponent α, as a clear signature of vacuum electron acceleration as a predominant physical mechanism whereby the energy of the laser driver is transferred to THz radiation. For strongly relativistic laser fields, on the other hand, WTHz(I0{lambda }_{0}^{2}) closely follows the scaling dictated by the relativistic electron laser ponderomotive potential {mathscr{F}}_{{text{e}}}, converging to WTHz ∝ {I}_{0}^{1/2}{lambda }_{0} for very high I0, thus indicating the decisive role of relativistic ponderomotive charge acceleration as a mechanism behind laser-to-THz energy conversion. Analysis of the electron distribution function shows that the temperature Te of hot laser-driven electrons bouncing back and forth between the plasma boundaries displays the same behavior as a function of I0 and λ0, altering its scaling from (I0λ02)α to that of {mathscr{F}}_{{text{e}}}, converging to WTHz ∝ {I}_{0}^{1/2}{lambda }_{0} for very high I0. These findings provide a clear physical picture of THz generation in relativistic and subrelativistic laser plasmas, suggesting the THz yield WTHz resolved as a function of I0 and λ0 as a meaningful measurable that can serve as a probe for the temperature Te of hot electrons in a vast class of laser–plasma interactions. Specifically, the α exponent of the best (I0λ02)α fit of the THz yield suggests a meaningful probe that can help identify the dominant physical mechanisms whereby the energy of the laser field is converted to the energy of plasma electrons.

Comparison of different laser pulse envelopes with frequency chirp for efficient electron acceleration in vacuum

In the present manuscript, we have investigated the effect of chirped laser pulse envelope to study electron acceleration in vacuum. For this purpose, we have chosen two different pulse shapes, i.e trapezoidal pulse envelope and Sin4 pulse envelope. Electron has been injected axially to the front of the tested envelopes. In all calculations, the front end of each pulse is presumed to have caught up with the electron at t = 0 at the coordinate origin. The relativistic Newton-Lorentz equations of motion of electron in the field of the laser pulse have been analytically and numerically solved. By optimizing laser and frequency chirp parameters, the energy gain of the order of GeV is obtained, and it has been noticed that under the similar range of phases (0 to 2π) and laser intensity parameter (a0 = 3), trapezoidal pulse envelope shows better result than Sin4 pulse envelope on effective electron acceleration in vacuum.

Optimizing direct laser-driven electron acceleration and energy gain at ELI-NP

We study and discuss electron acceleration in vacuum interacting with fundamental Gaussian pulses using specific parameters relevant for the multi-PW femtosecond lasers at ELI-NP. Taking into account the characteristic properties of both linearly and circularly polarized Gaussian beams near focus we have calculated the optimal values of beam waist leading to the most energetic electrons for given laser power. The optimal beam waist at full width at half maximum correspond to few tens of wavelengths, $\Delta w_0=\left\{13,23,41\right\}\lambda_0$, for increasing laser power $P_0 = \left\{0.1,1,10\right\}$ PW. Using these optimal values we found an average energy gain of a few MeV and highest-energy electrons of about $160$ MeV in full-pulse interactions and in the GeV range in case of half-pulse interaction.

Role of laser pulse asymmetry in electron acceleration in vacuum in the presence of an axial magnetic field

The role played by temporal asymmetry in a linearly polarized laser pulse on the acceleration of an electron in vacuum in the presence of an axial magnetic field has been investigated. The temporal shapes of the laser pulses considered here are Gaussian, positive skew (sharp rise and slow fall), and negative skew (slow rise and sharp fall). Since the pulse amplitude rises sharply in the case of positive skew, the electron experiences a strong intensity gradient during its interaction with the laser pulse, which strengthens the ponderomotive force. On the other hand, the electron experiences a gradual rise in pulse amplitude for a longer time duration in the case of negative skew. The electron energy is observed to be highest for a pulse with negative skew at low laser intensities and for a pulse with positive skew at high laser intensities. In the presence of an axial magnetic field, electron energy is observed to be highest for a pulse with positive skew at both low and high laser intensities.

Enhanced electron acceleration by a chirped tightly focused laser in vacuum in the presence of axial magnetic field

The paper presents a scheme of vacuum electron acceleration due to tightly focused linearly polarized (LP) frequency chirped laser in the presence external magnetic field. The focused terawatt chirped laser pulse and the external axial magnetic field enable the electron of few MeV initial energy to attain high energy in GeV range, hence, explore the possibility of efficient electron acceleration. This can be achieved by optimizing the focused terawatt chirped laser and axial magnetic field parameters for resonance, which is realized between the electron and electric field of the tightly focused laser pulse. The frequency chirp plays a crucial role in enforcing resonance condition for longer duration and the applied magnetic field strongly enforces the electron to remain in the accelerating phase, thereby, both factors are equally imperative for accomplishing high electron energy gain in GeV. The presence of optimum axial magnetic field (~8.5 MG) along with optimum value of linear frequency chirp for laser intensity 1.38 × 1020 W/cm2 results in electron beam with energy ~5.78 GeV. During acceleration process, electron energy gain is highly sensitive to the initial phase of laser along with the frequency chirp and magnetic field. Electron trajectories in the influence of frequency chirp and magnetic field are also analyzed.

Optimizing the electron acceleration in vacuum by chirped ultrashort laser pulse using particle swarm method

AbstractEfficient electron acceleration by a linearly chirped ultrashort laser pulse in vacuum is investigated using the particle swarm optimization method. By applying this method for optimizing the initial parameters of the laser pulse, a pronounced increase in final energy gain of the electron is obtained compared to that expected from the successive optimization method. Our results also suggest that the value of the optimal chirp parameter is independent of laser polarization and the energy gain could be insensitive to the sign of this parameter when the initial phase is optimally adjusted. In addition, utilizing the chirped laser pulse with optimized conditions for acceleration of an electron bunch reveals that the energy spectrum is shifted to considerably higher energies and the spatial distribution is significantly improved in a polarization-dependent manner.

Direct electron acceleration for diagnostics of a laser pulse focused by an off-axis parabolic mirror

We develop a theoretical basis for a new method of high-intensity ultrashort laser pulse diagnostics via vacuum electron acceleration from an ultrathin foil. A laser pulse is focused by an off-axis parabolic mirror, which has practical interest for most experiments with high-intensity pulses. The field description is based on Stratton–Chu integrals, which allow covering all focusing ranges up to the diffraction limit where the six-component laser field is correctly described. The theoretical approach uses a test particle method applicable for quite thin foils and rarefied gases, where the plasma fields do not substantially affect electron acceleration. The diagnostic method is to use measurements of angular-spectrum characteristics of laser accelerated or scattered electrons to compare them with the theory developed here. The proposed method can diagnose not only the intensity but also the quality of a laser pulse.

Effect of temporal asymmetry of the laser pulse on electron acceleration in vacuum

Abstract We explore the electron dynamics in a Gaussian laser pulse to assess the contribution of the temporal parameters to the mechanism of vacuum laser acceleration. Our numerical study reveals that a considerable nonzero energy gain can be achieved through a spatio-temporally controlled electron injection. Moreover, three-dimensional optimization of the electron’s injection angle suggests that the highest energy gain is obtained by using a sideways injection scheme. We also present the dependence of the electron energy gain on the laser polarization by comprehensively comparing all possible polarization states. It is found that the temporal sensitivity of the electron injection is determined by the polarization of the laser pulse. In addition, it is shown that although the energy gain is maximized in linearly polarized short laser pulses, circularly polarized laser pulses with longer duration would also lead to comparable energy gains but with much less temporal sensitivity for electron injection. To address the technical feasibility of the acceleration procedure under the mentioned optimized conditions, an experimental setup is proposed.

Electron acceleration from rest to GeV energy by chirped axicon Gaussian laser pulse in vacuum in the presence of wiggler magnetic field

This paper presents a scheme of electron energy enhancement by employing frequency - chirped lowest order axicon focussed radially polarised (RP) laser pulse in vacuum under the influence of wiggler magnetic field. Terawatt RP laser can be focussed down to ∼5μm by an axicon optical element, which produces an intense longitudinal electric field. This unique property of axicon focused Gaussian RP laser pulse is employed for direct electron acceleration in vacuum. A linear frequency chirp increases the time duration of laser-electron interaction, whereas, the applied magnetic wiggler helps in improving the strength of ponderomotive force v→×B→ and periodically deflects electron in order to keep it traversing in the accelerating phase up to longer distance. Numerical simulations have been carried out to investigate the influence of laser, frequency chirp and magnetic field parameters on electron energy enhancement. It is noticed that an electron from rest can be accelerated up to GeV energy under optimized laser and magnetic field parameters. Significant enhancement in the electron energy gain of the order of 11.2 GeV is observed with intense chirped laser pulse in the presence of wiggler magnetic field of strength 96.2 kG.