Toytman I, Silbergleit A, Simanovski D, Palanker D
Hansen Experimental Physics Laboratory, Stanford University, 452 Lomita Mall, Stanford, California 94305, USA.
Phys Rev E Stat Nonlin Soft Matter Phys. 2010 Oct;82(4 Pt 2):046313. doi: 10.1103/PhysRevE.82.046313. Epub 2010 Oct 27.
Transparent biological tissues can be precisely dissected with ultrafast lasers using optical breakdown in the tight focal zone. Typically, tissues are cut by sequential application of pulses, each of which produces a single cavitation bubble. We investigate the hydrodynamic interactions between simultaneous cavitation bubbles originating from multiple laser foci. Simultaneous expansion and collapse of cavitation bubbles can enhance the cutting efficiency, by increasing the resulting deformations in tissue, and the associated rupture zone. An analytical model of the flow induced by the bubbles is presented and experimentally verified. The threshold strain of the material rupture is measured in a model tissue. Using the computational model and the experimental value of the threshold strain one can compute the shape of the rupture zone in tissue resulting from application of multiple bubbles. With the threshold strain of 0.7 two simultaneous bubbles produce a continuous cut when applied at the distance 1.35 times greater than that required in sequential approach. Simultaneous focusing of the laser in multiple spots along the line of intended cut can extend this ratio to 1.7. Counterpropagating jets forming during collapse of two bubbles in materials with low viscosity can further extend the cutting zone-up to approximately a factor of 1.5.
利用聚焦紧密区域内的光击穿，超快激光能够精确切割透明生物组织。通常，通过逐次施加脉冲来切割组织，每个脉冲会产生一个单独的空化泡。我们研究了源自多个激光焦点的同步空化泡之间的流体动力学相互作用。空化泡的同步膨胀和坍塌能够通过增加组织中的变形以及相关的破裂区域来提高切割效率。本文提出并通过实验验证了由空化泡诱导的流动的分析模型。在模型组织中测量了材料破裂的阈值应变。利用计算模型和阈值应变的实验值，可以计算出施加多个空化泡后组织中破裂区域的形状。当阈值应变为0.7时，两个同步空化泡在距离比逐次施加所需距离大1.35倍时施加，可产生连续切割。沿着预定切割线在多个点同时聚焦激光可将该比例扩展至1.7。在低粘度材料中两个空化泡坍塌过程中形成的反向射流可进一步扩展切割区域——可达约1.5倍。
