标题： 钽薄膜上的高效超快光声转换 显示英文标题

标题： Efficient ultrafast photoacoustic transduction on Tantalum thin films

摘要： 通过超快激光激发在薄金属膜中产生纳米声学应变在材料科学、成像和医学应用中被广泛使用。最近的研究表明，与贵金属如银相比，过渡金属如钛表现出增强的光声转换特性。本工作展示了实验结果和模拟，证明在所有过渡金属中，钽表现出优越的光声特性。本文介绍了通过飞秒激光脉冲聚焦在沉积在硅基底上的薄钽膜上产生纳米声学应变的实验。纳米声学应变通过泵浦-探测瞬态反射率进行测量，该方法捕捉由光子-声子相互作用产生的布里渊振荡。观察到的布里渊振荡与钽薄膜的光声转换效率相关，并与钛薄膜的性能进行比较，明确展示了钽的优越光声转换效率。这些发现得到了计算结果的支持，这些计算利用双温模型结合热机械有限元分析，研究了激光诱导应变及其在这些薄金属膜/基底系统中的传播。最后，讨论了金属换能器-基底声阻抗匹配的作用，并提出了在晶体基底结构中生成适当调制的声脉冲序列的可能性，用于开发用于{\gamma }-射线生成的晶体波荡器。 显示英文摘要

摘要： Nano-acoustic strain generation in thin metallic films via ultrafast laser excitation is widely used in material science, imaging and medical applications. Recently, it was shown that transition metals, such as Titanium, exhibit enhanced photoacoustic transduction properties compared to noble metals, such as Silver. This work presents experimental results and simulations that demonstrate that among transition metals Tantalum exhibits superior photoacoustic properties. Experiments of nano-acoustic strain generation by femtosecond laser pulses focused on thin Tantalum films deposited on Silicon substrates are presented. The nano-acoustic strains are measured via pump-probe transient reflectivity that captures the Brillouin oscillations produced by photon-phonon interactions. The observed Brillouin oscillations are correlated to the photoacoustic transduction efficiency of the Tantalum thin film and compared to the performance of Titanium thin films, clearly demonstrating the superior photoacoustic transduction efficiency of Tantalum. The findings are supported by computational results on the laser-induced strains and their propagation in these thin metal film/substrate systems using a Two-Temperature Model in combination with thermo-mechanical Finite Element Analysis. Finally, the role of the metal transducer-substrate acoustic impedance matching is discussed and the possibility to generate appropriately modulated acoustic pulse trains inside the crystalline substrate structures for the development of crystalline undulators used for {\gamma}-ray generation is presented.