Generation of mega-electron-volt electron beams by an ultrafast intense laser pulse

Mega-electron-volt (MeV) electron emission from the interaction of an ultrafast (τ∼29 fs), intense (>10^18 W/cm^2) laser pulse with underdense plasmas has been studied. A beam of MeV electrons with a divergence angle as small as 1° is observed in the forward direction, which is correlated with relativistic filamentation of the laser pulse in plasmas. A novel net-energy-gain mechanism is proposed for electron acceleration resulting from the relativistic filamentation and beam breakup. These results suggest an approach for generating a beam of femtosecond, MeV electrons at a kilohertz repetition rate with a compact ultrafast intense laser system.