“…In these schemes, ponderomotive force plays the basic role, it can directly accelerate the electrons or excite a large amplitude plasma wave that can accelerate the electrons. The ponderomotive acceleration has been intensively investigated theoretically and experimentally, and compared with other acceleration methods (Nakamura, 2000;Nakamura et al, 2008;Lotov, 2001;Balakirev et al, 2001Balakirev et al, , 2004Geddes et al, 2004;Faure et al, 2004;Mangles et al, 2004;Reitsma et al, 2005;Li et al, 2004;Reitsma & Jaroszynski, 2004;Hoffmann et al, 2005;Mourou et al, 2006;Joshi, 2007;Hora, 2006Hora, , 2007Hora et al, 2009;Shi, 2007;Nickles et al, 2007;Chen et al, 2008;Kulagin et al, 2008;Limpouch et al, 2008). A fast moving electron at the front of the pulse can gain large energies when its velocity acquires a value greater than the group velocity of the laser before reaching the pulse peak.…”