Spin injection across interfaces driven by ultrashort optical pulses on femtosecond timescales constitutes a new way to design spintronics applications. Targeted utilization of this phenomenon requires knowledge of the efficiency of non‐equilibrium spin injection. From a quantitative comparison of ab initio time‐dependent density functional theory and interface‐sensitive, time‐resolved non‐linear optical experiment, the spin injection efficiency (SIE) at the Co/Cu(001) interface is determined, and its microscopic origin, i.e., the influence of spin‐orbit coupling and the interface electronic structure, is discussed. Moreover, we theoretically predict that the SIE at ferromagnetic–metal interfaces can be optimized through laser pulse and materials parameters, namely the fluence, pulse duration, and substrate material.

Spin injection across interfaces driven by ultrashort optical pulses on femtosecond timescales constitutes a new way to design spintronics applications. Targeted utilization of this phenomenon requires knowledge of the efficiency of non-equilibrium spin injection. From a quantitative comparison of ab-initio time-dependent density functional theory and interface-sensitive, time-resolved non-linear optical experiment, we determine the spin injection efficiencies (SIE) across ferromagnetic/metal interfaces and discuss their microscopic origin, i.e. the influence of spin-orbit coupling and the interface electronic structure. Moreover, we find that the SIE can be optimized through laser pulse and materials parameters, namely the fluence, pulse duration, and substrate material.