Background

Transient grating spectroscopy (TGS) is a laser-ultrasonic method allowing measurement of the surface acoustic wave (SAW) velocity in an examined material for a given direction of the wave vector.

Objective

We explore the capability of TGS for determination of shear elastic coefficients (\(c^\prime\) and \(c_{44}\)) of strongly anisotropic cubic materials.

Methods

TGS is tested on a set of single crystals with an anisotropy factor up to \(A=25\). Using a numerical simulation based on a Ritz-Rayleigh approach, we show that strong anisotropy may lead to significant coupling of SAWs with bulk shear waves, which complicates TGS measurements in specific directions. Based on the obtained TGS data, we discuss the possibility of also using the TGS technique for assessing the longitudinal elastic coefficient (\(c_L\)).

Results

Despite the energy focusing and other effects originating from the strong anisotropy, the TGS method can be used to reliably determine the directional dependence of the SAW velocity in these materials, and the resulting experimental datasets are sufficient for inverse determination of both the soft shear elastic constant (\(c^\prime\)) and the hard shear elastic constant (\(c_{44}\)). The longitudinal coefficient can be determined with lower accuracy.

Conclusion

TGS is a suitable experimental tool for contactless characterization of strongly anisotropic materials.

中文翻译：

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瞬态光栅光谱法对强各向异性材料的激光超声表征

背景

瞬态光栅光谱法（TGS）是一种激光超声方法，可以在给定的波矢方向上测量被检材料中的表面声波（SAW）速度。

目的

我们探索了TGS测定强各向异性立方材料的剪切弹性系数（\（c ^ \ prime \）和\（c_ {44} \））的能力。

方法

TGS在一组各向异性系数高达\（A = 25 \）的单晶上进行测试。使用基于Ritz-Rayleigh方法的数值模拟，我们显示出强各向异性可能会导致声表面波与体剪切波的显着耦合，从而使沿特定方向的TGS测量变得复杂。基于获得的TGS数据，我们讨论了也使用TGS技术评估纵向弹性系数（\（c_L \））的可能性。

结果

尽管能量聚焦和其他来自强各向异性的影响，TGS方法仍可用于可靠地确定这些材料中SAW速度的方向依赖性，并且所得的实验数据集足以反过来确定软剪切弹性常数（\（c ^ \ prime \））和硬剪切弹性常数（\（c_ {44} \））。可以以较低的精度确定纵向系数。

结论

TGS是用于强各向异性材料的非接触式表征的合适实验工具。