Time-resolved optical observation of spin-wave dynamics

We have created a nonequilibrium population of antiferromagnetic spin waves in Cr2O3, and characterized its dynamics, using frequency- and time-resolv ed nonlinear optical spectroscopy of the exciton-magnon transition. We obse rve a time-dependent pump-probe line shape, which results from excitation i nduced renormalization of the spin-wave band structure. We present a model that reproduces the basic characteristics of the data, in which we postulat e the optical nonlinearity to be dominated by interactions with long-wavele ngth spin waves, and the dynamics to be due to spin-wave thermalization.