Declercq Nico F, Polikarpova Nataliya V, Voloshinov Vitaly B, Leroy Oswald, Degrieck Joris
George W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, 801 Ferst Drive, Atlanta, GA 30332-0405, USA.
Ultrasonics. 2006 Dec 22;44 Suppl 1:e833-7. doi: 10.1016/j.ultras.2006.05.113. Epub 2006 Jun 6.
The anisotropic feature of most crystals, involves a direction dependent wave velocity for each of the possible modes. Paratellurite (Tellurium dioxide) is extraordinary because, for one of the propagation modes, i.e. the quasi shear horizontal (QSH) mode, the anisotropy is exceptional. This results, on the one hand in a very strong directional dependent sound velocity and on the other hand, in a low wave velocity in certain directions, resulting in a high figure of merit for the acousto-optical interaction. In the case of inhomogeneous waves, the slowness surfaces change their shape and magnitude, for all crystals. However, for paratellurite, this effect is again extraordinary. As soon as a relatively small inhomogeneity is considered, the sound velocity for the QSH mode becomes really exceptionally anisotropic, resulting in a slowness surface that is almost spherical, covered by pins. The velocity corresponding to those 'pins', is much lower than in the case of homogeneous plane waves, which is very promising for the future development of acousto-optic cells involving an even higher figure of merit.
大多数晶体的各向异性特征，涉及每种可能模式下与方向相关的波速。亚碲酸盐（二氧化碲）很特别，因为对于其中一种传播模式，即准水平剪切（QSH）模式，其各向异性非常显著。一方面，这导致声速具有很强的方向依赖性，另一方面，在某些方向上波速较低，从而使声光相互作用的品质因数很高。对于所有晶体而言，在非均匀波的情况下，慢度面会改变其形状和大小。然而，对于亚碲酸盐来说，这种效应再次显得非同寻常。一旦考虑到相对较小的不均匀性，QSH模式的声速就会变得极具各向异性，从而形成一个几乎呈球形、布满“针状物”的慢度面。与这些“针状物”对应的速度，比均匀平面波情况下的速度低得多，这对于未来开发具有更高品质因数的声光器件非常有前景。
