固体界面上光致弹性波驱动的微小物体纳米运动
Nanomotion of micro-objects driven by light-induced elastic waves on solid interfaces
摘要：
最近有报道说，纳秒光脉冲诱导的弹性波可以用来驱动摩擦固体界面上的微物体的纳米运动，这对于使用微小光学力的传统技术是一个挑战性的任务。在该技术中，涉及的主要物理量/参数是：光脉冲的时间宽度和能量、热加热和冷却时间、摩擦力和弹性波。尽管有一些基于微纤维系统的实验观察，但没有微观理论，该理论揭示了这些量如何协同地使微观物体运动，并推导出潜在的操纵原理。在这篇文章中，一个全面的理论分析-集中在上述列出的物理量，并通过一个单摩擦点模型结合数值模拟照明-建立教学澄清的物理。我们的研究结果揭示了这种技术中的两个基本因素：（1）使用短光脉冲快速热膨胀压倒性的摩擦阻力和（2）在热加热和冷却的时间尺度不对称积累净滑动距离。此外，我们研究的影响，空间分布的摩擦超出了单摩擦点的考虑，并显示“拔河”般的摩擦拉伸的驱动过程。鉴于这些见解，我们积极预测，这种基于弹性波的操纵原理可以直接转化为光学芯片上的微/纳米级光波导，并提出了一个实用的设计。我们希望这些结果提供理论指导正在进行的努力，光学操纵固体界面上的光致弹性波。
英文摘要：
It has been recently reported that elastic waves induced by nanosecond light pulses can be used to drive nano-motion of micro-objects on frictional solid interfaces, a challenging task for traditional techniques using tiny optical force. In this technique, the main physical quantities/parameters involved are: temporal width and energy of light pulses, thermal heating and cooling time, friction force and elastic waves. Despite a few experimental observations based on micro-fiber systems, a microscopic theory, which reveals how these quantities collaboratively enable motion of the micro-objects and derives what the underlying manipulation principles emerge, is absent. In this article, a comprehensive theoretical analysis--centralized around the above listed physical quantities, and illuminated by a single-friction-point model in conjunction with numerical simulations--is established to pedagogically clarify the physics. Our results reveal the two essential factors in this technique: (1) the use of short light pulses for rapid thermal expansion overwhelming friction resistance and (2) the timescale asymmetry in thermal heating and cooling for accumulating a net sliding distance. Moreover, we examine the effects of spatially distributed friction beyond the single-friction-point consideration, and show "tug-of-war"-like friction stretching in the driving process. Given these insights, we positively predict that this elastic-wave-based manipulation principle could be directly translated to micro/nano-scale optical waveguides on optical chips, and propose a practical design. We wish that these results offer theoretical guidelines for ongoing efforts of optical manipulation on solid interfaces with light-induced elastic waves.
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