It indicates that the direction of ray axis and optical axis is identical by discussing the uniaxial crystal at last.

最后对一轴晶进行了讨论，结果表明此时光轴方向与光线轴方向一致。

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In many instances the thickness of the optical axis direction of crystal as a important physical parameter needs to be confirmed, so it is necessary to accurately measure the crystal thickness.

在许多情况下，需要确定晶体光轴方向厚度这一重要的物理参数，为此就需要精确测量出晶体的厚度。

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