We present a new mechanism of energy gain of electrons accelerated by a laser pulse. It is shown that when the intensity of an ultrafast intense laser pulse decreases rapidly along the direction of propagation, electrons leaving the pulse experience an action of ponderomotive deceleration at the descending part of a lower-intensity laser field than acceleration at the ascending part of a high-intensity field, thus gain net energy from the pulse and move directly forward. By means of such a mechanism, a megaelectronvolt electron beam with a bunch length shorter than 100 fs could be realized with an ultrafast (<=30 fs), intense (> 10^(19) W/cm2) laser pulse.
© 2005 Chinese Optics Letters
Xiaofang Wang, Quandong Wang, and Baifei Shen, "Forward acceleration and generation of femtosecond, megaelectronvolt electron beams by an ultrafast intense laser pulse," Chin. Opt. Lett. 1, 50-52 (2003)