Intensity dependence of nonsequential double ionization of aligned asymmetric molecules

The electron correlation in nonsequential double ionization (NSDI) from aligned HeH+ molecules by intense laser pulses at various intensities has been investigated with the three-dimensional classical ensemble model. The results show that the correlated emission from NSDI for the parallel alignment is asymmetric. By back analysis the contribution of Coulomb focusing from H+ to this asymmetry has been also demonstrated besides the permanent dipole moment of the HeH2+ molecule. Moreover, the asymmetry of correlated emissions enhances sharply with decreasing laser intensity. This is attributed to the intensity dependence of the effects of the permanent dipole moment of the HeH2+ molecule and Coulomb focusing from H+ on the recollision dynamics. Besides the two electrons involved in NSDI of HeH+, molecules aligned parallel to the laser polarization are more likely to exit the molecule into the opposite hemispheres compared with the perpendicular alignment at some laser intensities, which is different from the case of symmetric molecules.