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 in x and p x space 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.