Potential and energy of the monoenergetic electrons in an alternative ellipsoid bubble model

Abstract

The electron acceleration in the bubble regime is considered during the intense laser-plasma interaction. The presented ellipsoid cavity model is more consistent than the previous spherical model, and it explains the monoenergetic electron trajectory more accurately. At the relativistic region, the maximum energy of electrons in the ellipsoid model is about $24%$ more than the spherical model, and this is confirmed by PIC and the measured experimental results reported here. The electron energy spectrum is also calculated, and it is found that the energy distribution ratio of electrons $\ensuremath{\Delta}E/E$ for the ellipsoid model in the here reported condition is about $11%$ which is less than the one third that of the spherical model. It is in good agreement with the experimentally measured value in the same condition. In this regime, the parameters of the quasi-monoenergetic electrons output beam can be described more appropriately. In this work, 10 TW from 16.6 TW, 500 mJ, and 30-fs laser pulse was focused on the best matched point above a 2-mm-diameter pulsed He gas jet to obtain a stable ellipsoid bubble. Laser intensity of $1.42\ifmmode\times\else\texttimes\fi{}{10}^{19}$ W cm${}^{\ensuremath{-}2}$ corresponding to a normalized vector potential of ${a}_{0}=2.6$ focused in a 100-$\ensuremath{\mu}$m${}^{2}$ spot at the focal point and 1 mm above the edge of the gas jet with an electron density of $1\ifmmode\times\else\texttimes\fi{}{10}^{19}$ cm${}^{\ensuremath{-}3}$ accelerates electrons to the relativistic velocities. The obtained monoenergetic electron energy spectrum is properly explained by the ellipsoid model introduced here.