Senegačnik Matej, Kunimoto Kohei, Yamaguchi Satoshi, Kimura Koki, Sakka Tetsuo, Gregorčič Peter
Faculty of Mechanical Engineering, University of Ljubljana, Aškerčeva 6, 1000 Ljubljana, Slovenia.
Department of Energy and Hydrocarbon Chemistry, Kyoto University, Nishikyo, Kyoto 615-8510, Japan.
Ultrason Sonochem. 2021 May;73:105460. doi: 10.1016/j.ultsonch.2021.105460. Epub 2021 Jan 9.
Laser ablation in liquids is growing in popularity for various applications including nanoparticle production, breakdown spectroscopy, and surface functionalization. When laser pulse ablates the solid target submerged in liquid, a cavitation bubble develops. In case of "finite" geometries of ablated solids, liquid dynamical phenomena can occur inside the bubble when the bubble overflows the surface edge. To observe this dynamics, we use diffuse illumination of a flashlamp in combination with a high-speed videography by exposure times down to 250 ns. The developed theoretical modelling and its comparison with the experimental observations clearly prove that this approach widens the observable area inside the bubble. We thereby use it to study the dynamics of laser-induced cavitation bubble during its expansion over a sharp-edge ("cliff-like" 90°) geometry submerged in water, ethanol, and polyethylene glycol 300. The samples are 17 mm wide stainless steel plates with thickness in the range of 0.025-2 mm. Bubbles are induced on the samples by 1064-nm laser pulses with pulse durations of 7-60 ns and pulse energies of 10-55 mJ. We observe formation of a fixed-type secondary cavity behind the edge where low-pressure area develops due to bubble-driven flow of the liquid. This occurs when the velocity of liquid overflow exceeds ~20 m s. A re-entrant liquid injection with up to ~40 m s velocity may occur inside the bubble when the bubble overflows the edge of the sample. Formation and characteristics of the jet evidently depend on the relation between the breakdown-edge offset and the bubble energy, as well as the properties of the surrounding liquid. Higher viscosity of the liquid prevents the generation of the jet.
液体中的激光烧蚀在包括纳米颗粒生产、击穿光谱学和表面功能化等各种应用中越来越受欢迎。当激光脉冲烧蚀浸没在液体中的固体靶材时，会形成一个空化气泡。对于烧蚀固体的“有限”几何形状，当气泡溢出表面边缘时，气泡内部会出现液体动力学现象。为了观察这种动力学，我们将闪光灯的漫射照明与高速摄像相结合，曝光时间低至250纳秒。所建立的理论模型及其与实验观察结果的比较清楚地证明，这种方法拓宽了气泡内部的可观测区域。因此，我们用它来研究激光诱导的空化气泡在浸没于水、乙醇和聚乙二醇300中的尖锐边缘（“悬崖状”90°）几何形状上膨胀时的动力学。样品是宽度为17毫米的不锈钢板，厚度在0.025 - 2毫米范围内。通过脉冲持续时间为7 - 60纳秒、脉冲能量为10 - 55毫焦的1064纳米激光脉冲在样品上诱导气泡。我们观察到在边缘后方形成了一种固定型的二次空穴，由于气泡驱动的液体流动，该区域会形成低压区。当液体溢出速度超过约20米/秒时会发生这种情况。当气泡溢出样品边缘时，气泡内部可能会发生速度高达约40米/秒的再入液体注入。射流的形成和特性显然取决于击穿边缘偏移与气泡能量之间的关系，以及周围液体的性质。液体的较高粘度会阻止射流的产生。
