On Time Dependence of Magnon Damping in Short Pulses
Magnon relaxation is due to its scattering on thermal quasiparticles. It is clear that if the pulse length is shorter than the time of phase mixing, then the damping is absent. If the length of the pulse is longer than the time of phase mixing, the magnon damping can be obtained from kinetic equation (KE). To find the time dependence of the magnon damping it is necessary to derive KE to the second order in perturbation taking a fast alteration of magnon amplitudes into account.