Laser wakefield and direct laser acceleration of electron in plasma bubble regime with circularly polarized laser pulse

With a circularly polarized (CP) Gaussian laser pulse, we examine theoretically the acceleration of electrons due to a combined effect of laser wakefield (LW) and direct laser (DL) in the plasma bubble regime. The CP laser pulse is ideal for DLA, since it allows for better electron trapping in the plasma bubble regime than a linearly polarized (LP) laser pulse. As a result of a CP laser pulse propagation in z direction, the electrons are accelerated in longitudinal direction by the accelerating field ( W z ) and focused in the transverse direction by the focusing fields ( W x , W y ). The density of plasma medium is about ∼ 1.8 × 10 18 cm - 3 which is from a 99.9 % He / 0.1 % N 2 neutral mix, laser pulse duration is 30 f s and wavelength 0.8 μ m . A bubble radius of over 20 μ m is achieved with a CP laser pulse at an intensity on the order of a 0 = 7 ( ∼ 2.14 × 10 20 W / cm 2 ), although the same can be achieved with an LP laser at a significantly higher intensity. The electron energy gain with a CP laser pulse appears to be above 3 GeV at this intensity. CP laser pulse appeared with a lower transverse emittance and a higher energy gain than an LP laser pulse of the same intensity. In comparison to LP laser pulse, CP laser pulse appears to have a more effective acceleration mechanism for LWFA with DLA in the plasma-bubble regime.