Crystal symmetry and polarization of high-order harmonics in ZnO
Crystal symmetry and polarization of high-order harmonics in ZnO
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DOI：
10.1088/1361-6455/ab470d
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发表时间：
2019-11-28
影响因子：
1.6
通讯作者：
Lin, C. D.
中科院分区：
文献类型：
--
作者：
Jiang, Shicheng;Gholam-Mirzaei, Shima;Lin, C. D.
我们对线偏振红外激光脉冲对氧化锌产生的高次谐波的偏振特性进行了理论和实验研究。实验发现，对于所有的奇次谐波，平行极化和垂直极化与晶体取向的关系几乎是相同的，但它们与偶次谐波有很大的不同，偶次谐波也表现出很小的次序依赖性。一维双带模型与线性耦合激发模型相结合，能够解释观察到的极化行为，包括低次谐波。我们进一步注意到，在许多其他晶体中也报道了相同的奇/偶数阶对比度，尽管谐波被认为是通过完全不同的机制产生的。我们证明了这种普适性是由晶体对称性决定的，而不是由特定的机制决定的。因此，谐波的偏振测量为确定晶体轴线以及监测晶体在变形时的超快变化提供了一种强大的纯光学方法。此外，还研究了调和的椭圆性。结果表明，通过改变样品的键结构，可以精确地调谐固体高次谐波的椭圆度。
We carried out a joint theoretical and experimental study of the polarization of high-order harmonics generated from ZnO by intense, linearly-polarized, infrared laser pulses. Experimentally we found that the dependence of parallel and perpendicular polarizations on the crystal orientation for all odd harmonics are nearly identical, but they are quite different from even harmonics which also show little order dependence. A one-dimensional two-band model, combined with a linear coupled excitation model, is shown to be able to explain the observed polarization behavior, including low-order harmonics. We further note that the same odd/even order contrast have been reported in a number of other crystals, despite that the harmonics were perceived to be generated via entirely different mechanisms. We demonstrated that this universality is governed by crystal symmetry, not by specific mechanisms. Thus, polarization measurements of harmonics offers a powerful pure optical method for determining the crystal axes as well as monitoring their ultrafast changes when crystals are undergoing deformation. In addition, the ellipticity of harmonic has been studied. It shows that ellipticity of high-order harmonics from solids can be tuned precisely by changing the bond structure of the sample.