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

Vacuum laser acceleration of relativistic electrons using plasma mirror injectors

“…1D Analytical calculations [3] show that for relativistic electrons, the maximum energy gain from this process is ∆E ∝ mc 2 γ 0 a 2 0 , where γ 0 is the electron initial Lorentz factor, and a 0 is the normalized laser vector potential, m the electron mass, and c the vacuum light velocity. Reaching high energy gains thus requires high initial energies γ 0 1 and/or ultrahigh laser amplitudes (a 0 1).In contrast with the large body of theoretical work published on this vacuum laser acceleration (VLA) of electrons to relativistic energies, experimental observations have largely remained elusive [12][13][14][15][16][17] -sometimes even controversial [18,19]-and have so far not demonstrated significant energy gains. This is because VLA occurs efficiently only for electrons injected in the laser field with specific initial conditions that are extremely challenging to fulfill experimentally [9].…”

Investigations of Field Dynamics in Laser Plasmas with Proton Imaging

“…To describe the electric fields for all times and the temporal evolution of the densities also for x < 0, numerical methods have to be applied. In [46,47] an expression for the field at the front has been found: 30) with τ F = ω pi t/ √ 2e E . For t = 0 and ω pi ≫ 1 this expression is similar to the formulas discussed above (see also [45]).…”

“…Due to the fact that for a focused laser pulse an axial magnetic field B x = ∂Ay ∂z exists, a force in the z-direction of the same order as the y-component of the ponderomotive force will act. Thus, the electrons are scattered radially symmetrical [17,[27][28][29][30].…”

Comment on “Electron acceleration by a short laser beam in the presence of a long-wavelength electromagnetic wave” [J. Appl. Phys. 102, 056106 (2007)]

“…Previous experimental results have shown that the electrons have only achieved an energy of 1 MeV from a laser beam with k 0 ¼ 1:056 lm and a 0 ¼ 3 in free space when no extra modulating laser field was applied. [7][8][9][10] According to the similar acceleration model analytically studied by our group several years ago, an upper limit of the energy an electron can get from laser fields in free space 2 is about Dc % 200, where the same parameters as the original paper are adopted. It is even far lower than 250 MeV.…”