Novel mechanism of electron injection into acceleration regime during the high intense laser pulse interaction with clusters

Fukuda, Yuji; Akahane, Yutaka; Aoyama, Makoto; Kiriyama, Hiromitsu; Yamakawa, Koichi; Mori, Michiaki; Kando, Masaki; Kotaki, Hideyuki; Masuda, Shinichi*; Echkina, E. Yu.*; Inovenkov, I. N.*; Koga, J. K.; Bulanov, S. V.; Tajima, Toshiki

In this study, using a cluster jet containing micron-sized Ar clusters, we present for the first time experimental results and supporting calculations of the generation of collimated relativistic electrons up to 58 MeV accelerated during the interaction of a 23-fs laser pulse at a laser intensity of W/cm. The resulting spectrum does not fit a Maxwellian distribution, but is well described by a two-temperature Maxwellian. Two dimensional particle-in-cell simulations demonstrate that the lower energy electrons are accelerated by the wake field being injected during the plasma wave breaking. The high energy electrons are injected in the laser pulse interaction with the clusters, and then they gain their energy during the direct acceleration by the laser pulse.