The tunneling ionization of an electron from a $p$ state in a highly charged ion in the relativistic regime is investigated in a linearly polarized strong laser field. In contrast to the case of an $s$ state, the tunneling ionization from the $p$ state is spin asymmetric. We single out two reasons for the spin asymmetry: first, the difference of the electron energy Zeeman splitting in the bound state and during tunneling, and second, the relativistic momentum shift along the laser propagation direction during the under-the-barrier motion. Due to the latter, those states are predominantly ionized where the electron rotation is opposite to the electron relativistic shift during the under-the-barrier motion. We investigate the dependence of the ionization rate on the laser intensity for different projections of the total angular momentum and identify the intensity parameter that governs this behavior. The significant change of the ionization rate originates from the different precession dynamics of the total angular momentum in the bound state at high and low intensities.

• Received 13 October 2014

DOI:https://doi.org/10.1103/PhysRevA.90.063416