  Coherent excitation of magnons is conventionally achieved through Raman
scattering processes, in which the difference-frequency components of the
driving field are resonant with the magnon energy. Here, we describe mechanisms
by which the sum-frequency components of the driving field can be used to
coherently excite magnons through two-particle absorption processes. We use the
Landau-Lifshitz-Gilbert formalism to compare the spin-precession amplitudes
that different types of impulsive stimulated and ionic Raman scattering
processes and their sum-frequency counterparts induce in an antiferromagnetic
model system. We show that sum-frequency mechanisms enabled by linearly
polarized driving fields yield excitation efficiencies comparable or larger
than established Raman techniques, while elliptical polarizations produce only
weak and circularly polarizations no sum-frequency components at all. The
mechanisms presented here complete the map for dynamical spin control by the
means of Raman-type processes.
