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题名	飞秒激光与透明材料相互作用若干新现象研究
作者	翟凯旋
学位类别	硕士
答辩日期	2015
授予单位	中国科学院上海光学精密机械研究所
导师	程亚
关键词	超快激光 激光微加工 纳米光栅 空气激光 分子隧穿电离
其他题名	On some new phenomena in the interactions of femtosecond laser with transparent material
中文摘要	根据激光参数和材料性质的不同，超快激光脉冲聚焦到透明块体材料内部会引发一系列有趣的效应，比如纳米孔的产生、周期纳米光栅的形成、折射率改变、材料组分的重新分布, 还有一些物质新相的产生等等。其中，纳米光栅是一种块体材料内部形成的自组织的亚波长的周期纳米结构，可以由紧聚焦的线偏振飞秒激光诱导产生。由于纳米光栅的特征尺寸远小于入射光波长，它为纳米光子学和纳流体提供了很大的潜在的应用。飞秒激光直写诱导纳米光栅已经在石英玻璃和其他掺杂玻璃内部得到了广泛地证实和应用。但是目前制备的纳米光栅结构存在着纵向分辨率低，横向和纵向光栅形貌不均匀，单位体积光栅相位延迟小等问题，极大阻碍了纳米光栅的进一步应用。最近，以多孔玻璃作为衬底的纳米级通道已经被报道，而在这过程中周期性中空纳米光栅阵列的产生还没有得到足够的重视。多孔玻璃具有大量的纳米孔隙结构，飞秒激光在其内部进行烧蚀加工，可以直接形成独特的中空纳米结构；不仅如此，多孔玻璃内部诱导的纳米光栅形貌的观测不需要后续的化学腐蚀处理，完整地保留了纳米光栅的形貌特征，为纳米光栅的精确制备提供了很好的反馈。多孔玻璃为纳米光栅研究和在微光学和微流体上的应用拓展了极好的平台。 此外，当超快激光聚焦到大气中，通过对大气远程泵浦会在泵浦区域产生的方向性的激射，即空气激光。空气激光作为一种新的超快非线性的光学现象已经引起了很大的关注，它可以产生方向性极好的高亮度，窄带的相干激射，空气激光的发现为提高远程探测的精确度和灵敏度以及大气中污染物识别提供了巨大的前景。空气激光可以分为两类 ：放大的自发辐射和种子放大。对于种子放大而言，激光行为只在中性氮气分子和氮气离子的前向被观测到。其中，隧穿电离诱导的氮气离子激光的泵浦机制还没有完全被弄清。 本文主要研究上述飞秒激光与透明材料相互作用的若干新现象。基于上述分别提到的两个问题，本文分为两部分，主要内容对应如下： 1. 为了解决前面所述的纳米光栅制备中存在的问题，充分利用前面所述的多孔玻璃的独特优势，我们以多孔玻璃为基底，利用纳米光栅的自组织效应，通过栅格式的激光直写扫描，将光栅结构在横轴和纵轴都进行了很好的空间上的延展。实验过程中采用高数值孔径物镜聚焦和狭缝光束整形，从而提高了焦斑处激光强度分布在横向的均匀性，缩短了纵轴方向上的焦斑的瑞利长度。利用本方法，我们成功制备了大规模均匀的高纵向精度的中空纳米光栅阵列。 2. 为了充分弄清氮气离子激光的泵浦机制，我们实验上展示了圆偏振飞秒激光泵浦下353.3 nm, 353.8 nm and 354.9 nm光谱线处的激光行为。这三条光谱线分别对应于B^2 ∑_u^+ (v’=5,4,3)→ X^2 ∑_g^+ (v=4,3,2) 跃迁。我们利用泵浦探测机制观察到了这三条激光谱线处激光压强相关的增益动力学性质。从而从实验上证实了电子碰撞激发是这三条光谱线处 N_2^+ 激光实现粒子数反转的重要原因。
英文摘要	Irradiation of intense ultrafast laser pulses inside bulk transparent materials leads to a series of interesting phenomena, such as formation of nanovoids and periodic nanogratings, refractive index change, glass constituent redistribution, and formation of new phase of matter. Among them, nanogratings are composed of self-assembled sub-wavelength periodic nanostructures which can be induced by tightly focused, linearly polarized femtosecond laser beam. Because their feature size is much less than the wavelength of the incident light, nanogratings have great potential in the applications of nanophotonics and nanofluidics. The formation of nanogratings by femtosecond laser direct writing has been achieved not only in fused silica, but also in doped silica. Although many polarization sensitive elements have been demonstrated (e.g. polarization diffractive grating, polarization converter, five-dimensional optical memory, etc.) based on the subwavelength nanogratings, some technical barriers (e.g. low spatial resolution in the longitudinal direction, inhomogeneous distribution of their morphologies, weak retardation per unit volume, etc.) still remain. Recently, by uniquely employing a porous glass as the substrate, single nanochannels with sub-50 nm feature sizes have been reported. The porous glass contains a large amount of uniformly distributed nanopores. Irradiated by intense femtosecond laser, periodic hollow nanocracks can be induced inside the focus volume. Thus, porous glass provides us an ideal platform for developing new applications of nanogratings in microoptics and microfluidics. Besides, lasing actions has been observed from the atmosphere irradiated by ultrafast laser. It has recently attracted significant attention as a novel ultrafast nonlinear light-matter interaction phenomenon. It provides promising potential for enhancing precision and sensitivity in remote detection and identification of pollutants in atmosphere. Generally, air lasers can be divided into two categories: amplified spontaneous emission and seed amplification. For the latter category, lasing actions have only been observed in neutral and ionic nitrogen molecules in the forward direction. But the pumping mechanism behind the tunnel ionization-induced nitrogen molecular ion lasers has not been completely clarified. In this thesis we focus on several new phenomena in the interactions of femtosecond laser with porous glass and air molecules. According to the two topics discussed above, the thesis is divided into two parts as follows: We have developed a method for large-scale and high-precision fabrication of nanogratings by employing the porous glass as the substrate. We demonstrate that self-organized nanocracks can be uniformly extended in porous glass along both the transverse and longitudinal directions. By use of a slit shaping technique, we obtained simultaneously a highly homogeneous distribution of laser intensity in the transverse direction and a short Rayleigh length of the laser beam along the longitudinal direction. By raster scanning of the focused laser beam in the sample, we have successfully fabricated large-scale homogeneous hollow periodic nanocracks arrays with high longitudinal precision inside porous glass. To fully understand the pumping mechanism behind the tunnel ionization-induced nitrogen molecular ion lasers, we experimentally investigate N_2^+ lasing actions at the wavelengths of 353.3 nm, 353.8 nm and 354.9 nm using a circularly-polarized femtosecond laser. The three laser lines correspond to B^2 ∑_u^+ (v’=5,4,3)→ X^2 ∑_g^+ (v=4,3,2) transitions, respectively. Particularly, we reveal the pressure-dependent gain dynamics of these lasing actions from highly excited vibrational states with a pump-probe scheme. Our experimental results confirm that electron collisional excitation plays an important role in establishment of population inversion of N_2^+ lasing at these wavelengths.
语种	中文
内容类型	学位论文
源URL	[http://ir.siom.ac.cn/handle/181231/16910]
专题	上海光学精密机械研究所_学位论文
推荐引用方式 GB/T 7714	翟凯旋. 飞秒激光与透明材料相互作用若干新现象研究[D]. 中国科学院上海光学精密机械研究所. 2015.

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