Femtceecond laserinduced nano-manipulation inside transparent materials

我们利用飞秒激光脉冲的干涉场或偏振特性，在各种材料内部实现了无表面损伤的周期性纳米结构化。这些研究成果都是基于飞秒激光脉冲具有超高的光子强度和超短的脉冲宽度的特点，在激光辐照下产生的光子与等离子体激元相互作用的基础上取得的。特别地，激光能量可以在电子和声子之间的耦合达到热力学平衡状态之前被注入到材料中。在熔融石英的情况下，通过飞秒单激光束照射，垂直于激光偏振方向自组织具有200 nm间距和20 nm宽度的周期性纳米结构。这种周期性的纳米结构（即纳米光栅）是由氧缺陷的密度调制组成的，氧缺陷区的玻璃成分由SiO_2改变为SiO_1.6。我们也证实了T ...更多信息 在TeO_2晶体中，周期性空洞在垂直于光场偏振方向的平面内形成并排列。我们推测，由于Te-O的结合能较弱，熔点较低（733 ℃），在TeO_2晶体内部形成了空洞。另一方面，在包括碱金属和碱土金属的多组分玻璃的情况下，不能形成偏振相关纳米光栅结构，而作为改性剂元素的Na和Ca元素扩散远离焦点。为了揭示纳米光栅结构的形成机理，我们研究了激光强度对纳米光栅结构的影响。从系统的实验中，我们已经证实，纳米光栅的间距从100到400 nm的激光能量密度的增加而变化。我们解释了纳米光栅的形成与激光辐照过程中等离子体的形成有关，特别是激光脉冲辐照过程中电子等离子体温度是纳米光栅形成的重要因素。在这些基础研究的基础上，我们在玻璃内制作了光栅、起偏器、光衰减器等集成微光学器件。少

We achieved the periodic nanostructuring inside various materials without surface damage by using interference field or polarizing properties of femtosecond laser pulse. These achievements were based on the interaction between the photon and plasmon induced by the laser irradiation, because the femtosecond laser pulses have together features of ultra high photon intensity and ultra fast pulse duration. Especially, laser energy can be injected into a material before the coupling between an electron and a phonon reaches a state of thermodynamic equilibrium. In the case of fused silica, a periodic nanostructure with a pitch of 200 nm and a width of 20 nm was self-organized perpendicular to the laser polarization direction by the femtosecond single laser beam irradiation. This periodic nanostructure (viz. nanograting) consisted of the density modulation of the oxygen defects, and then the glass composition in the oxygen defect regions are modified from SiO_2 to SiO_1.6. We also confirmed t … More hat the periodic voids were formed and aligned in the plane perpendicular to the polarization of the light field in the case of a TeO_2 crystal. We speculate that due to the weaker binding energy of Te-O and its lower melting point of 733 ℃, a void was formed inside TeO_2 crystal. On the other hand, in the case of multicomponent glass including alkaline metals and alkaline earth metals, the polarization-dependent nanograting structure can not be formed, while Na and Ca elements, which are modifier elements, diffused away from the focal point. In order to reveal the formation mechanism of nanograting structure we investigated how nanograting structure was affected according to the laser intensity. From the systematic experiments, we have confirmed that the pitch of nanograting was changed from 100 to 400 nm with increasing laser fluence. We interpreted that the nanograting formation was related to the plasma formation during laser irradiation, especially, the electron plasma temperature during laser pulse irradiation was the important factor for the nanograting formation. Based on these basic researches, we fabricated the integrated micro optical devices such as grating, polarizer, and optical attenuator inside glass. Less