  The surprising discovery of ultrafast demagnetization -- where electric field
of femtosecond laser pulse couples to electrons of a ferromagnetic (FM) layer
causing its magnetization vector {\em to shrink while not rotating}, is also
assumed to be accompanied by generation of spin current in the direction
orthogonal to electric field. However, understanding of the microscopic origin
of such spin current 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. Here we connect the standard pumping
phenomena driven by microwave precession of magnetization vector replacing
periodic time-dependence of magnetization precession with nonperiodic
time-dependence of demagnetization, as obtained from experiments on
ultrafast-light-driven Ni layer. Applying time-dependent nonequilibrium Green's
functions, able to evolve such setup with arbitrary time dependence, reveals
how demagnetization dynamics pumps both charge and spin currents in directions
both parallel and orthogonal to electric field of laser pulse, even in the
absence of spin-orbit coupling and thereby induced spin-to-charge conversion
mechanisms. Although pumped currents follow $dM_z/dt$ in some setups, this
becomes obscured when NM layers are disconnected and pumped currents start to
reflect from FM boundaries (as is the case of experimental setups). Finally, we
use the Jefimenko equations to compute electromagnetic radiation by charge
current pumped in 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.
