Nondipole effects in strong-field double ionization of aligned N ₂ molecules

We theoretically investigate nondipole effects in nonsequential double ionization (NSDI) of aligned N 2 molecules interacting with a strong, linearly polarized, 1600 nm mid-infrared laser field. Employing a three-dimensional classical ensemble model that fully incorporates nondipole effects, we calculate the sum momentum distributions of the two electrons along the laser propagation direction for both parallel and perpendicular molecular alignments at various intensities. The nondipole shift extracted from the observed peak deflections shows a distinct dependence on both molecular alignments and laser intensity. Trajectory analysis reveals that molecular alignment modulates the effective potential and Coulomb focusing arising from the two nuclei. This modulation, together with increasing intensity, alters the relative weights of three types of ionization events with different Lorentz forces, leading to distinct intensity-dependent behaviors in the two alignments. This work provides fundamental insights into alignment-dependent nondipole effects and paves a potential way for controlling nondipole effects in strong-field ionization of molecules.