Nakamura A, Shimojima T, Ishizaka K
RIKEN Center for Emergent Matter Science, Wako, Saitama 351-0198, Japan.
Struct Dyn. 2021 Apr 15;8(2):024103. doi: 10.1063/4.0000059. eCollection 2021 Mar.
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.
在本文中，我们基于有限元模拟研究了相对较薄（100纳米）和较厚（10000纳米）硅板中飞秒光脉冲诱导的应变动力学。在薄样品中，光脉冲几乎在空间上均匀激发，主要沿面外方向产生最低阶声共振模式的驻波。同时，横向传播的板波通过开放边缘变形在样品边缘发射。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，因此产生了沿面外方向传播的应变脉冲，同时伴随着通过边缘变形的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，包括非对称和高阶对称模式。我们的模拟定量地展示了实际硅板中面外和面内光致应变动力学，从板波形式到脉冲序列，这取决于诸如样品厚度、光穿透深度和声速等材料参数。
