  We demonstrate optical control of magnons using femtosecond laser pulses by
performing ab-initio real-time time-dependent density functional theory (TDDFT)
simulations. We predict that the spin-wave dynamics in Fe$_{50}$Ni$_{50}$ can
be manipulated by tailoring the applied laser pulse via three distinct
mechanisms: (1) element selective destruction of magnon modes depending on the
laser intensity, (2) delay dependent freezing of the magnon mode into a
transient non-collinear state (where delay is in the pulse peak with respect to
the start of simulations), and (3) optically induced inter sublattice transfer
(OISTR) driven renormalization of the optical magnon frequency. Harnessing such
processes would significantly speed up magnonic devices.
