Generation of high-energy electrons by a femtosecond terawatt laser propagating through a sharp downward density transition

We demonstrate by computer simulations the generation of high-energy electrons by using a femtosecond terawatt laser pulse propagating in a plasma with a sharp downward density transition. In the two-dimensional simulation, a 20-TW laser pulse with a pulse duration of 60 fs and a wavelength of 800 nm propagates through a plasma with a sharp density transition consisting of n0I=5×1018 cm−3 and n0II=0.75n0I. The simulation result demonstrates that a significant amount of electrons can be self-trapped and accelerated to an energy of 117 MeV over a distance of 0.62 mm by the ultrastrong nonlinear laser wake field. In addition, it has been found that the trapping dynamics is much different from the electron-beam-driven dynamics and that the energy spread of the trapped electrons can be reduced significantly by use of the density tapering method.