Sum-frequency excitation of coherent magnons

Ultrashort laser pulses can coherently excite quasiparticles with macroscopically large amplitudes. 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 frequency. Here, we describe mechanisms by which the sum-frequency components of the driving field can be used. We numerically simulate the spin-precession amplitudes that impulsive stimulated and ionic Raman scattering processes and their sum-frequency counterparts are able to induce in a model antiferromagnet with realistic experimental opto- and phono-magnetic coupling coefficients. We show that the sum-frequency excitation is possible via the (phonon) inverse Cotton-Mouton effect, but not the (phonon) inverse Faraday effect. These sum-frequency mechanisms operate at lower excitation energies than conventional techniques, and they complete the map of dynamical spin control pathways by the means of Raman-type mechanisms.