The surprising discovery of ultrafast demagnetization—where the electric field of a femtosecond laser pulse interacts with electrons of a ferromagnetic (FM) layer to cause its magnetization vector to shrink while not rotating, $M_z\left(t\right)/M_z(t=0)<1$—is also assumed to be accompanied by generation of spin current in the direction orthogonal to electric field. However, understanding the microscopic origin of such a spin current, its frequency spectrum, and how efficiently it can be converted into charge current as the putative source of THz radiation, is lacking despite nearly three decades of intense studies. Conversely, quantum transport theory rigorously explains how microwave-driven precession of a magnetization vector of fixed length $\mathbf{M}\left(t\right)$ leads to pumping of spin current into adjacent normal metal (NM) layers, sandwiching the FM layer to form two-terminal geometry without any applied bias voltage. Here we connect these two apparently disparate phenomena by replacing periodic time dependence of magnetization precession with nonperiodic time dependence of demagnetization, as obtained from experiments on an ultrafast-light-driven Ni layer, within the same two-terminal setup of standard spin pumping theory. Applying time-dependent nonequilibrium Green's functions, able to evolve such setup with arbitrary time dependence, predicts phenomenon of charge pumping by demagnetization dynamics, as well as spin, with such currents flowing in directions both parallel and orthogonal to the electric field of laser pulse. The pumping of charge current directly by ultrafast demagnetization dynamics occurs even in the absence of spin-orbit coupling (SOC) and, presumed to be necessary, spin-to-charge conversion via SOC. Although pumped currents follow $d{M}_z/dt$ in some setups, this becomes obscured when NM layers are disconnected and pumped currents start to reflect from FM boundaries (as in realistic experimental setups). Finally, we use the Jefimenko equations to compute electromagnetic radiation by charge current pumped in a disconnected setup during demagnetization, or later during its slow recovery, unraveling that radiated electric field only in the former time interval exhibits features in 0.1–30 THz frequency range probed experimentally or explored for applications of spintronic THz emitters.

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• Quantum transport
• Spin pumping
• Ultrafast demagnetization
• Maxwell's equations
• Nonequilibrium Green's function