The phase-lock dynamics of the laser wakefield acceleration with an intensity-decaying laser pulse

An electron beam with the maximum energy extending up to 1.8 GeV, much higher than the dephasing limit, is experimentally obtained in the laser wakefield acceleration with the plasma density of 3.5 x 10(18) cm(-3). With particle in cell simulations and theoretical analysis, we find that the laser intensity evolution plays a major role in the enhancement of the electron energy gain. While the bubble length decreases due to the intensity-decay of the laser pulse, the phase of the electron beam in the wakefield can be locked, which contributes to the overcoming of the dephasing. Moreover, the laser intensity evolution is described for the phase-lock acceleration of electrons in the uniform plasma, confirmed with our own simulation. Since the decaying of the intensity is unavoidable in the long distance propagation due to the pump depletion, the energy gain of the high energy laser wakefield accelerator can be greatly enhanced if the current process is exploited. (C) 2014 AIP Publishing LLC