Underdense Plasma Layer Research Articles

Electron bunch acceleration in the wake wave breaking regime

Results are presented from theoretical analysis and 2D PIC simulations of electron acceleration in a breaking wake plasma wave generated by a short intense laser pulse during its interaction with a finite-length underdense plasma layer. The high energy electron energy spectrum and transverse emittance are obtained. It is shown that, for laser pulse lengths above the plasma wake wavelength, the wakefield-accelerated electrons are further accelerated by the electromagnetic wave.

Simulation of electron bunch generation by an ultrashort-pulse high-intensity laser-driven wakefield

Electron acceleration due to a wakefield excited by a ultrashort-pulse intense laser propagating through a finite-length underdense plasma layer is studied by two-dimensional particle-in-cell simulation. The electron energy distribution is analyzed for moderate to high intensity. For the electron density, where the pulse length is almost half of the plasma wavelength, dramatic changes of the density structure occur with cavity and bunch formation with an increase in the laser intensity, also leading to the appearance of a fast electron component well confined in phase space. The analytical form of the fast electron energy spectrum is also presented.

Spectral and dynamical features of the electron bunch accelerated by a short-pulse high intensity laser in an underdense plasma

The results of the theoretical consideration and two-dimensional particle in cell simulation of electron acceleration with a short-pulse intense laser propagating through a finite length underdense plasma layer are presented. The fast electron energy spectrum and emittance are analyzed for moderate to high intensity and for different plasma density. It is shown that for laser pulse lengths above the plasma wake wavelength the wakefield accelerated electrons are further accelerated by the electromagnetic wave.

Electron acceleration by the short pulse laser in inhomogeneous underdense plasmas

Electron acceleration by the ponderomotive force of a laser pulse with duration less than the plasma wavelength in inhomogeneous underdense plasmas is studied by two-dimensional relativistic parallel particle-in-cell (PIC) code. Particular attention is paid to the mechanism of electron acceleration associated with the increasing group velocity of the laser pulse. In an underdense plasma layer with linearly descending density profile, the accelerated electrons move together with the laser pulse which propagates with increasing group velocity. In an inhomogeneous pre-plasma with linearly ramping density profile, as the incident laser propagates up the density gradient with decreasing group velocity, ponderomotive acceleration is reduced compared with the uniform pre-plasma. As the reflected laser propagates down the density gradient with increasing group velocity, the ponderomotive acceleration by the reflected laser is more effective due to increasing group velocity of the reflected light and the return currents induced by the incident laser light. Relativistic electrons with multi-tens-MeV energies are generated.

Acceleration of high-quality, well-collimated return beam of relativistic electrons by intense laser pulse in a low-density plasma

The mechanism of electron acceleration by intense laser pulse interacting with an underdense plasma layer is examined by one-dimensional particle-in-cell (1D-PIC) simulations. The standard dephasing limit and the electron acceleration process are discussed briefly. A new phenomenon, of short high-quality, well-collimated return relativistic electron beam with thermal energy spread, is observed in the direction opposite to laser propagation. The process of the electron beam formation, its characteristics, and the time-history inxandpxspace for test electrons in the beam, are analyzed and exposed clearly. Finally, an estimate for the maximum electron energy appears in a good agreement with simulation results.

A New Mechanism of Laser Absorption in a Sputtered Thin Plasma

Th is paper discusses the laser absorption in a thin underdense plasma layer, which is sputtered from a solid surface ablated by laser irradiation. An analysis expression of absorption efficiency is obtained, and two new absorption mechanisms are revealed. The first one is an unusual, but effective, wave-particle resonance absorption (which is different from the conventional Landau damping). The second one is a new, but much feeble, effect of the density and velocity gradient on the laser absorption. Enhancement of the sputtered velocity will increase the absorption efficiency of the laser, but non-homogeneity of the plasma will decrease it.

Ion explosion and multi-mega-electron-volt ion generation from an underdense plasma layer irradiated by a relativistically intense short-pulse laser.

Ion acceleration and expansion in the interaction of a relativistically intense short-pulse laser with an underdense plasma layer are investigated. Ion and electron dynamics are studied by a two-dimensional particle-in-cell simulation with the real mass ratio. It is shown that the longitudinal electric field induced by electron evacuation due to a large ponderomotive force or light pressure can accelerate ions to several MeV in the direction of the laser propagation. It is after the laser completely passes through the plasma layer that the ion explosion starts to be significant.

MeV ion generation by an ultra-intense short-pulse laser: application to positron emitting radionuclide production

A new method is proposed for producing 18F, a positron emitter, via 18O(p,n)18F reactions with fast protons from the interaction of a relativistically-intense short-pulse laser with an underdense plasma layer. The fast ion concentration contributing to the nuclear reaction is estimated on the basis of a two-dimensional particle-in-cell simulation. The instantaneous production rate of 18F is found to be two orders of magnitude larger than by the standard method using a cyclotron.

Perturbation calculation of the scattering of electromagnetic waves by an underdense plasma layer

A perturbation technique has been utilized to obtain the scattering of electromagnetic waves by an underdense plasma layer for Gaussian, sech2, and parabolic density distribution, and the calculations compared with accurate solutions. The results for the reflection are good at small values of plasma width, but (except for the parabolic case) decrease too rapidly at large plasma widths. The transmission coefficient is more difficult to calculate and, despite the presence of absorption, has a spurious rise to unity at large plasma widths. A Wentzel-Kramers-Brillouin calculation of the transmission yields fairly accurate results and with less labor than required by the perturbation method.