Diffraction of light by magnetoelastic waves

The diffraction of light at 1.15 microns has been observed from transverse magnetoelastic (ME) waves at a frequency of 1.1 GHz in a YIG bar. A shift in the Bragg diffraction angle was observed when the external magnetic field along the bar axis was varied in order to change the elastic and spin wave admixture. The waves were excited by a shear wave transducer, and were on the upper branch of the ME dispersion curves. The largest shift obtained experimentally was -3°, measured from the elastic limit of 9.5°. This required a field change of about 20 Oe. The shift was accompanied by a delay in the diffracted pulse of about 1μs, due to the change in the group velocity. The optical polarization properties indicate that both the elastic and spin wave parts of the ME wave were contributing to the diffraction through the photo-elastic effect and optical Faraday rotation, respectively. The diffracted signal in the magnetically shifted region was transient in nature, and showed strong saturation effects due to saturation of the ME wave.