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.