A thorough understanding of the electron-phonon, thermo-optic, and acoustic properties of materials is of paramount importance for many applications in materials science and advanced applications adopting laser-induced sound waves. Even though metals are usually opaque to light, optical methods for materials characterization can still be developed, especially in the high-frequency regime, where phonon dynamics governs the thermal, acoustic, and even optical properties of metals. Ultrafast laser pulses incident on metals can lead to the generation of coherent phonon wave packets with frequencies in the gigahertz to terahertz range, providing a means to study the material properties in this otherwise inaccessible frequency range. While this principle has been known, the complex interplay of light and matter in both the generation and detection of such ultrafast hypersound pulses has limited its use mainly to geometrical effects. Here, we demonstrate the quantitative characterization of a range of different material properties using laser-driven hypersound. We use all-optical generation and detection of hypersound pulses to sensitively probe the bulk properties of various metals. We introduce an advanced two-dimensional numerical model that captures the generation, propagation, and detection of these hypersound waves in full detail. The combination of experiment and simulation allows us to unravel and elucidate various physical effects that appear over a wide range of different time scales. Through least-squares fitting of the data to the simulation results, we extract quantitative information about the electron-phonon, thermo-optic, and acoustic properties of metal films, establishing the ability to use light as a sensitive probe for the study of opaque materials.

中文翻译：

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利用光驱动超音速分析金属的声子，光声和机械性能

对于材料科学中的许多应用以及采用激光感应声波的高级应用，透彻了解材料的电子声子，热光和声学特性至关重要。尽管金属通常对光不透明，但是仍然可以开发用于表征材料的光学方法，尤其是在高频范围内，其中声子动力学决定金属的热，声，甚至光学特性。入射到金属上的超快激光脉冲会导致产生相干声子波包，其频率在千兆赫兹至太赫兹范围内，从而提供了一种研究在此否则无法接近的频率范围内的材料特性的方法。虽然已经知道了这一原理，在这种超快超音脉冲的产生和检测中，光和物质之间的复杂相互作用已将其主要用于几何效应。在这里，我们演示了使用激光驱动的超音波对一系列不同材料特性的定量表征。我们使用全光生成和超音脉冲检测来灵敏地探测各种金属的整体性质。我们引入了一个高级的二维数值模型，该模型可以详细捕获这些超音波的产生，传播和检测。实验和模拟的结合使我们能够阐明和阐明在不同时间范围内出现的各种物理效应。通过将数据与模拟结果进行最小二乘拟合，