Optical Probing of Magnetoelastic Waves

Abstract

The use of an optical probe to observe magnetoelastic (ME) waves in yttrium iron garnet gives new information not obtainable by other methods. The interaction of the light with the elastic and magnetic parts of a transverse ME wave gives rise to some unusual polarization properties, which are explained by a simple theory of the diffraction. For the laser polarized parallel or perpendicular to the plane of diffraction, a relation is found between the laser polarization giving maximum diffracted intensity and the sign of the frequency shift of the diffracted light. For a frequency shift of given sign, the optimum laser polarization is reversed for waves on the quasielastic portions of the upper and lower branches of the ME dispersion curves. When the spin-wave component is larger (near the turning points in the bar), the optimum polarization is the same on both branches, contrary to the theory. This anomaly is probably due to the large amplitude of the ME signals used in the experiments.