The time-scale of nonlinear events driven by strong fields: can one control the spin coupling before ionization runs over?

An initially populated spin state of an ion chain interacting with an external field can decay via spin coupling or via ionization. Using a simple two-level Hamiltonian we investigate the relation between spin-coupling and ionization rate and identify conditions for an efficient spin-control via a non-resonant Stark effect by suppressing ionization. The results are confirmed in solving the time-dependent Schrodinger equation for the interaction of a laser field with a spin-coupled model system where two electrons and a nucleus move in a collinear configuration. It is thus shown, that quantum control of intersystem crossing can indeed be effective if the intensity of the external field and the accompanying Stark-shift is adjusted properly to the spin-coupling strength.