Time-Resolved Optical Observation of Spin-Wave Dynamics

We have created a nonequilibrium population of antiferromagnetic spin waves in Cr2O 3 , and characterized its dynamics, using frequency- and time-resolved nonlinear optical spectroscopy of the exciton-magnon transition. We observe a time-dependent pump-probe line shape, which results from excitation induced renormalization of the spin-wave band structure. We present a model that reproduces the basic characteristics of the data, in which we postulate the optical nonlinearity to be dominated by interactions with long-wavelength spin waves, and the dynamics to be due to spin-wave thermalization. (c) 1999 The American Physical Society