Effect of the ponderomotive scattering and injection position on electron-bunch injection into a laser wakefield

• Published in: Applied physics. B, Lasers and optics Lasers and optics, 2007-01, Vol.86 (1), p.41-47
• Main Authors: KHACHATRYAN, A. G, LUTTIKHOF, M. J. H, VAN GOOR, F. A, BOLLER, K.-J
• Format: Article
• Language: English
• Subjects: Charged-particle beams; Collection; Electromagnetism; electron and ion optics; Electrostatic, collective, and linear accelerators; Exact sciences and technology; Experimental methods and instrumentation for elementary-particle and nuclear physics; Femtosecond; Fundamental areas of phenomenology (including applications); Laser-driven acceleration; Laser-plasma acceleration of electrons and ions; Laser-plasma interactions; Lasers; Low energy; Nuclear physics; Physics; Physics of gases, plasmas and electric discharges; Physics of plasmas and electric discharges; Plasma (physics); Scattering; Spreads; Wavelengths
• ISSN: 0946-2171; 1432-0649
• DOI: 10.1007/s00340-006-2469-6

For the purpose of laser wakefield acceleration, it turns out that the injection of electron bunches longer than the plasma wavelength can also generate accelerated femtosecond bunches with a relatively low energy spread. This is of great interest because such injecting bunches can be provided, e.g., by photo cathode rf linacs. Here we show that when an e-bunch is injected into the wakefield, it is important to take into account the interaction of the injected bunch with the laser pulse in the vacuum region located in front of the plasma. We show that at low energies of the injected bunch, this leads to ponderomotive scattering of the bunch and results in a significant drop of the collection efficiency. For certain injection energies the ponderomotive scattering may result in a smaller energy spread in the accelerated bunch. It is found that the injection position in the laser wakefield plays an important role. Higher collection efficiency can be obtained for certain injection energies, when the bunch is injected in plasma at some distance from the laser pulse; the energy spread, however, is typically larger in this case. We also estimate the minimum trapping energy for the injected electrons and the length of the trapped bunch.