Phenomenological theory for coherent magnon generation through impulsive stimulated Raman scattering

We present a phenomenological theory for impulsive generation of coherent magnons in magnetic dielectrics through impulsive stimulated Raman scattering. Consideration is given to a lattice which has an arbitrary number of localized spins in each magnetic unit cell. A general expression for the modulation of optical dielectric permittivity by light-induced spin waves is derived and its symmetry properties with respect to time reversal are analyzed. A simple cubic ferromagnet and a rutile-type structure antiferromagnet are treated as examples of application of the theory. It is shown that the ellipticity of the spin precession, inherent to spin waves in antiferromagnets, leads to an enhancement of the amplitude of light-induced spin waves.