185 / 2023-04-15 15:38:37

Experimental studies on the electron acceleration and positron generation in the interaction of Petawatt femtosecond lasers with gas targets

极端光下的基础物理学 > QED效应和核物理-II

Ultra-intense femtosecond laser has advantages on generating high-energy electrons with large charges. These energetic electrons, interacting with secondary targets, can produceγ-photons and positrons with high brightness. These energetic particle sources also have broad applications in material detection, dynamic diagnosis and other fields. Toward to generating these energetic secondary radiation and particles based on the Petawatt femtosecond laser, however, there are still two problems to be overcome. The first is how to efficiently generate highly energetic electrons with large charges. The second is how to transport these energetic electrons to secondary target with high efficiency. In response to these two problems, we report the experimental studies on the electron acceleration and positron generation, which are conducted on the SILEX-II facility at the Laser Fusion Research Center of the Chinese Academy of Physics. It is observed that MeV electrons with a high charge of several tens of nC can be well generated by a 6J, 40fs laser interacting with a high-density gas jet. However, it is shown that the propagation of the highly charged electron beam is significantly inhibited because the electrons are reflected by the sheath potential in the density decreasing region of the gas target, thus leading to a low positron yield. Consequently, by using an integrated nozzle-converter design to eliminate the density falling ramp of the gas target such that the electron refluxing is inhibited, we observe a significant enhancement of positron yield (up to a factor of 15), finally reaching a positron yield of 5×10⁸/sr. This high-yield ultrashort MeV positron may have great potential toward the simulation of astrophysical pair plasma.