The ultrafast modulation of optical crystal birefringence, involving rapid deformations of crystalline lattices, holds significant scientific and technological importance. High-frequency coherent phonons, through transient perturbation of lattice order, have emerged as a powerful tool for modifying the properties of materials. Here, we systematically investigate coherent phonons in the asymmetric crystal directions [011], [110], and [100] of VO2/TiO2 heterostructures. Notably, in the (011)-VO2/TiO2 system, a remarkable shear mode coherent phonon signal was excited, exhibiting a marginally higher intensity compared to the longitudinal mode. By changing the probe light polarization, we observed a fascinating reversal in the birefringence sign induced by the giant coherent phonons. Density functional theory (DFT) calculations indicate that TiO2 possesses excellent photoelastic properties, with strong coherent phonons efficiently modulating refractive index anisotropy, accounting for this phenomenon. This finding provides novel insights into the development of ultrafast acousto-optic devices.

中文翻译：

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通过具有不对称 VO2/TiO2 异质结构的强相干声子工程进行双折射调制


光学晶体双折射的超快调制涉及晶格的快速变形，具有重大的科学和技术重要性。高频相干声子通过晶格序的瞬态扰动，已成为改变材料性能的有力工具。在这里，我们系统地研究了 VO2/TiO2 异质结构不对称晶体方向 [011]、[110] 和 [100] 上的相干声子。值得注意的是，在 (011)-VO2/TiO2 系统中，激发了显着的剪切模式相干声子信号，与纵模相比表现出稍高的强度。通过改变探测光的偏振，我们观察到巨大的相干声子引起的双折射符号发生了令人着迷的反转。密度泛函理论 (DFT) 计算表明，TiO2 具有优异的光弹性特性，具有强相干声子，可有效调制折射率各向异性，从而解释了这一现象。这一发现为超快声光器件的开发提供了新的见解。