Transformer ratio and pulse shaping in laser wakefield accelerator

We show that, in complete analogy to the electron-beam driven plasma wakefield accelerator (PWFA), an optimal transformer ratio can be attained in the laser driven laser wakefield accelerator (LWFA), by properly shaping the longitudinal profile of the driving laser pulse. The concept of transformer ratio in LWFA is introduced and the optimal laser pulse shape is derived in the linear regime of laser-plasma interaction. We show that in the linear regime of plasma perturbation the requirement for the laser pulse shape and the resultant optimal transformer ratio are identical for LWFA and PWFA concepts. (orig.)