In this paper, we investigate the femtosecond-optical-pulse-induced strain dynamics in relatively thin (100 nm) and thick (10 000 nm) silicon plates based on finite-element simulations. In the thin sample, almost spatially homogeneous excitation by the optical pulse predominantly generates a standing wave of the lowest-order acoustic resonance mode along the out-of-plane direction. At the same time, laterally propagating plate waves are emitted at the sample edge through the open edge deformation. Fourier transformation analysis reveals that the plate waves in the thin sample are mainly composed of two symmetric Lamb waves, reflecting the spatially uniform photoexcitation. In the thick sample, on the other hand, only the near surface region is photo-excited and thus a strain pulse that propagates along the out-of-plane direction is generated, accompanying the laterally propagating pulse-like strain dynamics through the edge deformation. These lateral strain pulses consist of multiple Lamb waves, including asymmetric and higher-order symmetric modes. Our simulations quantitatively demonstrate the out-of-plane and in-plane photoinduced strain dynamics in realistic silicon plates, ranging from the plate wave form to pulse trains, depending on material parameters such as sample thickness, optical penetration depth, and sound velocity.

中文翻译：

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硅薄板光致应变动力学的有限元模拟

在本文中，我们基于有限元模拟研究了相对较薄（100 nm）和较厚（10 000 nm）硅板中的飞秒光脉冲诱发应变动力学。在薄样品中，光脉冲几乎空间均匀的激发主要沿面外方向产生最低阶声共振模式的驻波。同时，通过开放边缘变形在样品边缘发射横向传播的板波。傅里叶变换分析表明，薄样品中的板波主要由两个对称的兰姆波组成，反映了空间均匀的光激发。另一方面，在厚样品中，只有近表面区域被光激发，因此产生沿面外方向传播的应变脉冲，伴随着通过边缘变形横向传播的脉冲状应变动力学。这些横向应变脉冲由多个兰姆波组成，包括不对称和高阶对称模式。我们的模拟定量地展示了现实硅板中的面外和面内光致应变动力学，范围从板波形到脉冲序列，具体取决于样品厚度、光学穿透深度和声速等材料参数。