Laser Pulse In Vacuum Research Articles

Comment on “Electron acceleration by a chirped Gaussian laser pulse in vacuum” [Phys. Plasmas 13, 123108 (2006)

Sohbatzadeh et al. [Phys. Plasmas 13, 123108 (2006)] have presented a scheme of vacuum electron acceleration by using a chirped Gaussian laser pulse. They assume a linear polarization of the laser pulse in this scheme. We point out that this might be an important assumption in their work and it can seriously influence the electron energy gain during laser acceleration. In this Comment, the circular polarization of a chirped laser pulse is employed and our results show higher electron energy gains.

Response to “Comment on ‘Electron acceleration by a chirped Gaussian laser pulse in vacuum’” [Phys. Plasmas 14, 044701 (2007)

Response to “Comment on ‘Electron acceleration by a chirped Gaussian laser pulse in vacuum’” [Phys. Plasmas 14, 044701 (2007)

Electron acceleration by a chirped Gaussian laser pulse in vacuum

Electron acceleration by a chirped Gaussian laser pulse is investigated numerically. A linear and negative chirp is employed in this study. At first, a simple analytical description for the chirp effect on the electron acceleration in vacuum is provided in one-dimensional model. The chirp mechanism is then extended to the interaction of a femtosecond laser pulse and electron. The electron final energy is obtained as a function of laser beam waist, laser intensity, chirp parameter, and initial phase of the laser pulse. It is shown that the electron final energy depends strongly on the chirp parameter and the initial phase of the laser pulse. There is an optimal value for the chirp parameter in which the electron acceleration takes place effectively. The energy gain increases with laser beam waist and intensity. It is also shown that the electron is accelerated within a few degrees to the axial direction. Emphasis is on the important aspect of the chirp effect on the energy gained by an electron from the electromagnetic wave.

Electron acceleration by a chirped short intense laser pulse in vacuum

Electron acceleration by a chirped short intense laser pulse has been studied in a vacuum. A linear frequency chirp ω(t)=ω0(1−αt) has been considered, where ω0 is the laser frequency at z=0 and α is frequency chirp parameter. Transverse electron momentum increases due to frequency chirp and the electron escapes from the laser pulse near the pulse peak. Longitudinal momentum also increases due to increase in longitudinal force. Retained electron energy is much higher with frequency chirp than that without frequency chirp. Retained energy peaks for a suitable value of α; the value of which decreases with laser intensity and initial electron energy.

Calculation of electromagnetic field components for a fundamental Gaussian beam

Using a perturbative method, we carefully calculate seventh- and ninth-order expressions for electromagnetic field components for a fundamental Gaussian beam (i.e., a focused TEM00 mode laser beam) propagating in the medium analogous to vacuum. The interaction of a single electron and a focused laser pulse in vacuum has a promising application in the design of a powerful electron accelerator which could compete with the traditional ones. For this, ninth-order accuracy in the expansion describing the focused laser beam is required. When the vector potential corresponds to polarization along the direction of propagation, the number of electromagnetic field components can be reduced from 5 or 6 to 3. Furthermore, we find two rules obeyed by all orders of the vector potential, which greatly simplify the calculation procedure of the vector potential order by order, and make it possible to investigate the behavior of high orders.

Properties of electron acceleration by a circularly polarized laser in vacuum

The dynamic characteristics of an electron accelerated by ultraintense circularly polarized laser pulses in vacuum following the capture and acceleration scenario were studied. Comparing them with that from the use of linearly polarized laser pulses, we found (i) that the acceleration channel is wider, leading to greater acceleration efficiency, and (ii) that the maximum energy gains rise much more slowly as the laser intensity increases. This slow rise is caused by the magnetic-field force, which weakens the longitudinal acceleration force at higher laser intensity.

Acceleration of a pre-accelerated electron by an ultra-short and ultra-intense laser pulse in vacuum

Acceleration of a pre-accelerated electron by an ultra-short and ultra-intense laser pulse in vacuum has been explored. The deceleration by the descending part of the laser pulse can be neglected when the pre-accelerated electron is accelerated by the ascending part of the pulse. Because the acceleration dist ance is much longer than for a initially stationary electron, the energy gain is much larger. The net energy gain can be up to 01GeV with a laser intensity of 1019W/cm2 and an initial electron energy of 45Me V. Final energy ga in of the electron as a function of its initial condition and laser parameters h as also been discussed.

Electron capture and violent acceleration by a tightly focused ultra-short ultra-intense laser pulse in vacuum

A low-energy relativistic free electron capture and violently acceleration by a tightly focused ultra-short ultra-intense laser pulse in vacuum is presented in this paper. The results show that the electron is mainly accelerated by the long itudinal ponderomotive force and the energy gain is sensitively dependent on the retarded time, initial energy and the incident angle of electron. On the other hand, the energy gain is not very sensitive to the pulse width when it is larger than 10λ.

Electron Acceleration by a Focused Gaussian Laser Pulse in Vacuum

By numerically solving the relativistic equations of motion of a single electron in laser fields modeled by a Gaussian laser beam, we get the trajectory and energy of the electron. When the drifting distance is comparable to or even longer than the corresponding Rayleigh length, the evolution of the beam waist cannot be neglected. The asymmetry of intensity in acceleration and deceleration leads to the conclusion that the electron can be accelerated effectively and extracted by the longitudinal ponderomotive force. For intensities above 1019 W μm2/cm2, an electron's energy gain about MeV can be realized, and the energetic electron is parallel with the propagation axis.

Formula omitted]-pair production by a focused laser pulse in vacuum

The probability of electron–positron pair creation by a focused laser pulse is calculated. For description of the focused laser pulse we use a 3-dimensional model of the electromagnetic field which is based on an exact solution of Maxwell equations. There exists two types of focused waves: e- and h-polarized waves with only either electric, or magnetic vector being transverse respectively. It is shown that pair production is possible only in e-polarized electromagnetic wave. The dependence of the pair production probability on the intensity of the laser pulse is obtained. It is argued that there exists a natural physical limit for attainable focused laser pulse intensities. This limit is posed by the pulse energy loss due to the effect of pair creation.

Laser microprocessing in a gas environment at a high repetition rate of ablative pulses

The parameters of laser ablation of channels in steel are studied in a wide range of nanosecond pulse repetition rates f (5 Hz ≤ f ≤ 200 kHz). It is found that for f ≥ 4 kHz, the results of ablation in air are identical to those obtained under the action of single laser pulses in vacuum. The experimental data as well as the estimates of the parameters of laser plasma and the gas environment in the region of the laser action lead to the conclusion that there exists a long-lived region of hot rarefied gas, known as a fire ball in the theory of explosions. The emerging rarefaction reduces the screening effect of the surface plasma formed under the action of subsequent pulses. This makes it possible to use lasers with a high pulse repetition rate for attaining ablation conditions close to the conditions in vacuum without complicating the technology of microprocessing by using vacuum chambers and evacuating pumps.

Interaction of an electron bunch with a laser pulse in vacuum

The output properties of electrons accelerated by the vacuum laser acceleration scheme CAS (capture and acceleration scenario) are addressed. The transport process of the electron bunch, the fraction of the CAS electrons of the incident electrons, the correlation of electron energy with position and scattering angle, the energy spectrum and angular distributions as well as the emittance of the outgoing electrons are studied at a laser intensity of a0=10. In addition, the effects of the laser intensity, beam width, and pulse duration on the properties of the output electrons are also examined. Physical explanations of those output characteristics are presented based on the mechanism behind the CAS scheme. The feasibility of CAS to become a realistic laser accelerator scheme is explored.

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.

Micro Electron Bunch Acceleration and Trapping by Intense Short Laser Pulse in Vacuum

We propose an electron bunch acceleration and trapping mechanism by an intense short laser pulse in vacuum. By using a short laser pulse obtained by the linear combination of a TEM10 mode and a TEM01 mode with the same amplitude and the relative phase shift of π/2, the electrons are accelerated in the longitudinal direction by a longitudinal ponderomotive force, and the electrons divergence in the transverse direction can be suppressed by a transverse ponderomotive force. In order to analyze the electron motion, the relativistic equation of motion including a relativistic radiation damping effect is solved. In our calculations, the electron is accelerated to 179 [MeV] with an acceleration gradient of 5.12 [GeV/m] at the laser intensity of 1.23×1018 [W/cm2]. The rms emittances of the electron bunch accelerated are (1.06, 1.21, 0.348) [mm mrad] in the x, y and z directions, and the spatial size of this electron bunch accelerated in the radial and longitudinal directions are 856 [μm] and 11.7 [μm], respectively.

Acceleration of electron bunches by intense laser pulse in vacuum

This paper addresses the output characteristics of real electron bunches accelerated with ultra-intense laser pulse in vacuum by the capture & acceleration scenario (CAS) scheme (see, e.g., Phys. Rev. E66 (2002) 066501). Normally, the size of an electron bunch is much larger than that of a tightly focused and compressed laser pulse. We examine in detail the features of the intersection region, the distribution of electrons which can experience an intense laser field and be accelerated to high energy. Furthermore, the output properties of the accelerated CAS electrons, such as the energy spectra, the angular distributions, the energy–angle correlations, the acceleration gradient, the energy which can be reached with this scheme, the emittances of the outgoing electron bunches, and the dependence of the output properties on the incident electron beam qualities such as the emittance, focusing status, etc. were studied and explained. We found that with intense laser systems and electron beam technology currently available nowadays, the number of CAS electrons can reach 10 4–10 5, when the total number of incident electrons in the practical bunch reaches ∼10 8. These results demonstrate that CAS is promising to become a novel mechanism of vacuum laser accelerators.

Synthesis efficiency of heavy carbon clusters from ETFE ablated by different numbers of laser pulse in vacuum

We have carried out mass spectral analysis of positive ions produced by laser ablation of a copolymer of ethylene and tetrafluoroethylene (ETFE: [CH 2CH 2CF 2CF 2] n ) in vacuum using time-of-flight mass spectrometry (TOF-MS). The surfaces of the ETFE targets irradiated by different numbers of laser pulse were analyzed by X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). Heavy carbon cluster ions C n + with n≥30 were observed in the mass spectra. The fractional abundance of heavy clusters in the mass spectrum decreased with the number of laser pulse. On the other hand, carbon became rich in the atomic composition of the laser-irradiated surface, and the eroded area on the surface increased with the number of laser pulse. From these results, it is suggested that the carbon-rich material surface results in the less efficient production of heavy carbon clusters. In addition, it is also suggested that clustering reactions in eroded craters do not contribute to the synthesis of heavy clusters.

Potential jump on a laser target

Various mechanisms of the appearance of a potential jump on a target irradiated by 10.6-μm laser pulses in vacuum are considered. It is shown that, in principle, the potential jump can be used to monitor the parameters of the laser pulses and measure the electron temperature of a laser plasma.

Electron acceleration by intense shock-like laser pulses in vacuum

With both analytical and numerical simulation methods, it is found that, by using an intense laser pulse with sharply rising or falling edges in vacuum, an electron can be accelerated to very high energies, which approaches the upper-limit of the energy predicted by the half-wavelength acceleration mechanism. Because the form factor of the laser pulse is like the shape of a shock wave, we call this kind of acceleration mechanism as shock-pulse-laser acceleration.

Electron acceleration by a laser pulse in vacuum

The acceleration of an electron by a circularly polarized, high-intensity ultrashort laser pulse in vacuum is studied. It appears that the energy of the electron can be accelerated significantly, and the electron moves almost along the propagation direction of the laser pulse.

Classical theory of nonlinear Compton scattering.

The covariant dynamics of a single classical electron subjected to the electromagnetic field of an intense, linearly polarized, ultrashort laser pulse in vacuum is studied in the context of the Dirac-Lorentz equation, which has long been suggested as a possible theory which includes radiative reaction. The Dirac-Lorentz equation is integrated numerically using Dirac{close_quote}s suggestion that the acausal (no runaway) solution should produce physically interesting consequences. This appears to be the case in our Compton scattering calculations, although the exact meaning of the results is not clear. {copyright} {ital 1996 The American Physical Society.}