Dynamic spatial variations of the `unconverted´ exit beam in the magnetostatic wave-optical interaction

The authors have observed in YIG (yttrium-iron-garnet) an effect apart from the anisotropic MSW (magnetostatic wave) optical collinear interaction which has a much wider bandwidth than the latter: about 500 MHz vs 10 MHz at MSW frequencies between 6 and 7 GHz. A slit placed in front of the detector profiles the film parallel to its width. It is found that the beam has a non-Gaussian component synchronous with the MSW modulation. The shape of this component depends on k_MSW, but there is usually one negative and one positive peak, as if light were being deflected from one part of the beam to another. When the whole beam is focused on the detector, these wideband features cancel, leaving the expected narrow peak associated with the anisotropic interaction. Changes in the profile shape are small as the input MSW power is varied between 2 and 20 dBm. This wideband effect may be due to isotropic MSW-optical interactions, but this is in doubt because the peak spreading does not appear to change with k _MSW in the unconverted exit beam