<title>Attenuation and diffraction measurements of shear acoustic waves in GaP above 4 GHz</title>

Abstract

GaP with shear acoustic mode in (110) direction is one of the few acousto-optic materials which are practical for the AO devices operating above several GHz frequencies. Low acoustic attenuation, low acoustic non-linearity, and high AO figure of merit of this mode in GaP provides remarkably large time-bandwidth products with small apertures and high enough diffraction efficiencies. In addition, the self- collimating (or low diffraction spreading) orientation of this mode in GaP allows selection of a smaller transducer height to improve further the AO diffraction efficiency and to increase the optical throughput with smaller channel spacing in multi-channel Bragg cells. Acoustic diffraction spreading and attenuation measurement in a shear mode GaP AO device operating at 4.2 GHz are reported here. Negligible acoustic beam diffraction spreading in this device allowed us to deduce accurate attenuation data for the shear mode. We measured 1.88 dB/cm-GHz<SUP>2</SUP> or 0.77 dB/microsecond- GHz<SUP>2</SUP> acoustic attenuation for this mode.