  Sub-picosecond magnetisation manipulation via femtosecond optical pumping has
attracted wide attention ever since its original discovery in 1996. However,
the spatial evolution of the magnetisation is not yet well understood, in part
due to the difficulty in experimentally probing such rapid dynamics. Here, we
find evidence of rapid magnetic order recovery in materials with perpendicular
magnetic anisotropy via nonlinear magnon processes. We identify both
localisation and coalescence regimes, whereby localised magnetic textures
nucleate and subsequently evolve in accordance with a power law formalism.
Coalescence is observed for optical excitations both above and below the
switching threshold. Simulations indicate that the ultrafast generation of
noncollinear magnetisation via optical pumping establishes exchange-mediated
spin currents with an equivalent 100% spin polarised charge current density of
$10^8$ A/cm$^2$. Such large spin currents precipitate rapid recovery of
magnetic order after optical pumping. These processes suggest an ultrafast
optical route for the stabilization of desired meta-stable states, e.g.,
isolated skyrmions.
