Intelligent Ultra Precision Microfabrication System with Pico Second Pulse Glass Laser

本研究的目的是开发一种基于超快激光的智能精密微加工系统。智能制造系统可以对加工现象进行预测。为了实现激光烧蚀现象的预测，进行了热力学分析和分子动力学模拟。在热力学分析中，考虑了蒸发潜热、蒸发过程中气液界面的位移、蒸发反冲压力和Marangoni力，分析了伴随蒸发的熔池流动。由于蒸发反冲压力降低了熔池表面，产生了孔洞。由于蒸发反冲压力产生的流动将熔融的金属推离到周围，因此在孔的周围产生了一个上升。这种流动在激光照射结束和上升生长后保持不变。在金属的分子动力学模拟中，发现有两种蒸发形式。一种是当脉冲宽度极短时发生的爆炸性蒸发。另一种是当脉冲宽度相对较长时发生的相对平静的蒸发。在前一个过程中，相对较大的颗粒分散。在后一过程中，散射粒子的尺寸相对较小。在对硅的三维分子动力学模拟中，发现激波在Si[111]方向的传播速度比在Si[100]方向的传播速度快。当脉冲宽度较长时，如5ps，Si(111)表面结构的熔合深度更深，这是因为原子在Si[111]方向上的排列是分层的，热更容易传递。另一方面，当脉冲宽度极短时，如0.2ps，熔合深度与表面结构无关，这是因为激光内部吸收的影响较大，而热传导的影响较小。

Purpose of this study is to develop an intelligent precision microfabrication system with ultrafast laser. An intelligent manufacturing system can predict the processing phenomena. In order to realize prediction of laser ablation phenomena, thermohydrodynamics analysis and molecular dynamics simulation were carried out. In thermohydrodynamics analysis, the flow of molten pool accompanied with evaporation was analyzed considering latent heat of vaporization, displacement of gas-liquid interface during evaporation, evaporation recoil pressure and Marangoni force. A hole is generated as a result that the surface of molten pool is lowered by evaporation recoil pressure. Because the flow caused by the evaporation recoil pressure pushes the molten metal away to the surroundings, a rising is generated at circumference of the hole. This flow is maintained after the laser irradiation is finished and the rising grows up. In the molecular dynamics simulation of metal, it was found that there are two types in evaporation form. One is the explosive evaporation that occurs when pulse width is extremely short. The other is the relatively calm evaporation that occurs when pulse width is comparatively long. In the former process, comparatively large particles scatter. In the latter process, the size of scattering particles is relatively small. In the three-dimensional molecular dynamics simulations of silicon, it was found that propagation velocity of shock wave in Si [111] direction is faster than that in Si [100] direction. When the pulse width is comparatively long such as 5 ps, fusion depth in Si(111) surface structure is deeper, because atomic arrangement in Si [111] direction is layered and heat is easier to transferred. On the other hand, when the pulse width is extremely short such as 0.2 ps, the fusion depth is independent of surface structure, because the influence of internal absorption for laser is larger and the effect of heat conduction is much smaller.