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Conical refraction of elastic waves in absorbing crystals

机译:吸收晶体中弹性波的圆锥折射

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The absorption-induced acoustic-axis splitting in a viscoelastic crystal with an arbitrary anisotropy is considered. It is shown that after "switching on" absorption, the linear vector polarization field in the vicinity of the initial degeneracy point having an orientation singularity with the Poincaré index n = ±1/2, transforms to a planar distribution of ellipses with two singularities n = ±1/4 corresponding to new axes. The local geometry of the slowness surface of elastic waves is studied in the vicinity of new degeneracy points and a self-intersection line connecting them. The absorption-induced transformation of the classical picture of conical refraction is studied. The ellipticity of waves at the edge of the self-intersection wedge in a narrow interval of propagation directions drastically changes from circular at the wedge ends to linear in the middle of the wedge. For the wave normal directed to an arbitrary point of this wedge, during movement of the displacement vector over the corresponding polarization ellipse, the wave ray velocity s runs over the same cone describing refraction in a crystal without absorption. In this case, the end of the vector moves along a universal ellipse whose plane is orthogonal to the acoustic axis for zero absorption. The areal velocity of this movement differs from the angular velocity of the displacement vector on the polarization ellipse only by a constant factor, being delayed by π/2 in phase. When the wave normal is localized at the edge of the wedge in its central region, the movement of vector s along the universal ellipse becomes drastically nonuniform and the refraction transforms from conical to wedge-like.
机译:考虑在具有任意各向异性的粘弹性晶体中吸收引起的声轴分裂。结果表明,在“开启”吸收之后,初始简并点附近的线性矢量极化场具有庞加莱指数n =±1/2的方向奇点,转换为具有两个奇点n的椭圆的平面分布=±1/4对应于新轴。在新的简并点和连接它们的自相交线附近研究了弹性波慢度表面的局部几何形状。研究了由吸收引起的经典折射圆锥形变。自相交楔形的边缘在传播方向的狭窄间隔中的波椭圆率从楔形端的圆形急剧变为楔形中间的线性。对于指向该楔形的任意点的法线,在位移矢量在相应的偏振椭圆上运动期间,射线速度s在同一圆锥上传播,描述了晶体在没有吸收的情况下发生折射。在这种情况下,矢量的末端沿通用椭圆移动,该椭圆的平面与声轴正交以实现零吸收。该运动的面速度与极化椭圆上的位移矢量的角速度仅相差一个常数因数,相位延迟了π/ 2。当波法线位于楔形的中心区域中时,矢量s沿通用椭圆的运动变得非常不均匀,并且折射从圆锥形变为楔形。

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