Assessment of material perfection and observation of vibration modes in lithium tantalate by X-ray topography

The crystalline perfection of LiTaO₃ samples was examined using synchrotron radiation X-ray topography. The two thickness shear modes existing in X-cut plates were observed using either conventional or stroboscopic topography. The fundamental fast shear mode and its anharmonics display strong trapping properties. The slow shear mode is not strongly trapped and extends far from the electroded region. In most cases, the fast shear mode and its anharmonics are coupled to plate modes. Using the time structure of the radiation of the synchrotron, it is shown that, in most instances, these coupled modes include progressive components with a large standing wave ratio. The existence of these progressive waves, characterized by a large amplitude, was observed in all the samples