Observation of strong correlation between quasimonoenergetic electron beam generation by laser wakefield and laser guiding inside a preplasma cavity

Abstract

We use a one-shot measurement technique to study effects of laser prepulses on the electron laser wakefield acceleration driven by relativistically intense laser pulses ($\ensuremath{\lambda}=790\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$, $11\phantom{\rule{0.3em}{0ex}}\mathrm{TW}$, $37\phantom{\rule{0.3em}{0ex}}\mathrm{fs}$) in dense helium gas jets. A quasimonoenergetic electron bunch with an energy peak $\ensuremath{\sim}11.5\phantom{\rule{0.3em}{0ex}}\mathrm{MeV}$ [$\ensuremath{\Delta}E∕E\ensuremath{\sim}10%$ (FWHM)] and with a narrow-cone angle $(0.04\ensuremath{\pi}\phantom{\rule{0.3em}{0ex}}\mathrm{mm}\phantom{\rule{0.2em}{0ex}}\mathrm{mrad})$ of ejection is detected at a plasma density of $8\ifmmode\times\else\texttimes\fi{}{10}^{19}\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}3}$. A strong correlation between the generation of monoenergetic electrons and optical guiding of the pulse in a thin channel produced by picosecond laser prepulses is observed. This generation mechanism is well corroborated by two-dimensional particle-in-cell simulations.