STRONG INFRARED-LIGHT SCATTERING FROM COHERENT SPIN WAVES IN YTTRIUM IRON GARNET

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Abstract
We report the first direct observation of strong Bragg‐scattered infrared light (1150 nm wavelength) from coherent spin waves (1.5 GHz). The maximum scattered‐light intensity is found to be at least five times stronger than that of longitudinal elastic waves of comparable power. The experiments were performed with an axially magnetized, single‐crystal YIG bar, with the axis oriented in a {100} plane at an angle of 22.5° from a 〈100〉 axis. The coherent spin waves were generated through efficient space‐gradient conversion from longitudinal elastic waves; the latter were excited from a sputtered ZnO transducer. The scattered‐light intensity is found to be dependent on the incident‐light polarization and the sign of frequency shift (Stokes or anti‐Stokes lines) and independent of the direction of the applied magnetic field. Previous theoretical calculations on light scattering from coherent spin waves are critically reviewed and revised. The new result appears to explain adequately not only the present experiments but also observations that previous authors have reported as ``anomalous''.