Intensity-dependent two-electron emission dynamics with orthogonally polarized two-color laser fields

Abstract

In this paper, we explore the intensity-dependent strong-field double ionization of Ne with orthogonally polarized two-color laser pulses consisting of 800- and 400-nm laser fields. The yield of ${\text{Ne}}^{2+}$ as a function of the relative phase $\mathrm{\ensuremath{\Delta}}\ensuremath{\phi}$ of the two colors experiences a qualitative transition as the laser intensity decreases from the saturation regime to the far-below-saturation regime. In the saturation regime, our simulations well reproduce the recent experimental observations [Phys. Rev. Lett. 112, 193002 (2014)]. Turning to the far-below-saturation regime, however, we find that the observed small knee structure totally disappears and the maximum yield of ${\text{Ne}}^{2+}$ is shifted by a $\ensuremath{\pi}/2$ phase. This is explained by the competition between the trajectory concentration effect and the $\mathrm{\ensuremath{\Delta}}\ensuremath{\phi}$-dependent ionization rate of the tunneling electron. The possibility of controlling over the two-electron emission direction along the 400-nm field through the laser intensity is also investigated. We show that the two-electron emission direction can be reversed by changing the laser intensity for some vales of $\mathrm{\ensuremath{\Delta}}\ensuremath{\phi}$, while this fails for some other values of $\mathrm{\ensuremath{\Delta}}\ensuremath{\phi}$.