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题名	飞秒激光在玻璃内部制备金属和半导体纳米晶体及其光学性能研究
作者	林耿
学位类别	博士
答辩日期	2012
授予单位	中国科学院上海光学精密机械研究所
导师	赵全忠
关键词	飞秒激光，玻璃，金属和半导体纳米晶体，量子点，光学性能
其他题名	Novel Metal and Semiconductor Nanocrystals in Glasses Induced by Femtosecond Laser and Their Optical Properties
中文摘要	飞秒激光微纳加工技术由于具有可突破衍射极限的加工分辨率和可对透明材料三维加工的能力使其在众多的精密加工技术中备受关注。它为实现器件的系统微型化、功能集成化和结构可调化提供了良好的解决方法，并已广泛应用于各种微光电子学器件的制备，同时也为强场物理、非线性光学和材料科学等基础学科提供丰富的实验和理论素材，进一步促进了这些交叉学科的发展。在飞秒激光微纳加工技术二十多年的发展历史中，早期的研究以及应用主要是关注于1 kHz飞秒激光与材料的相互作用，但是在近十年中，关于高重复频率(>100 kHz)飞秒激光微纳加工的实验以及物理机制引起了人们广泛的兴趣。与低重复频率(1 kHz)飞秒激光相比，高重复频率飞秒激光微纳加工最显著的特点是它的热累积效应，聚焦的高重复频率飞秒激光辐照到透明材料内部时可以产生一个局域化的高温场，利用这个高温场可以在透明材料内部诱导出各种热驱动的物理和化学变化。比如飞秒激光诱导玻璃中三维可控析出光功能晶体就是一个非常典型的例子。虽然飞秒激光诱导析晶的研究也开展的比较早，但还是不够深入，实现晶化的晶体种类也非常有限，缺乏系统性。 本论文对250 kHz高重复频率飞秒激光在玻璃中空间选择性诱导析出晶体进行了系统的研究，实现了多种新型纳米晶体的析出和控制，包括金属（Pb、Ga、Cu）、半导体（Si、Ge）和量子点（PbSe、PbTe等）。具体可分为以下几个方面： 1、提出了一种制备新型金属和半导体纳米晶体掺杂玻璃的普适方法。通过在玻璃原料中添加强的还原剂，如金属Al、Zn和碳粉等，使之在玻璃熔融过程中与玻璃成分中的氧化物如SiO2等发生氧化还原反应得到各种金属和半导体原子或原子团簇掺杂的母玻璃，再辅助以热处理过程便可析出各种金属和半导体纳米晶体(如Si、Ge、Pb、Ga等)。作为对比，未在原料中添加还原剂的玻璃在其他实验条件相同的情况下则不能析出各种纳米晶体，表明添加的还原剂在纳米晶体的析出中起着至关重要的作用。通过控制热处理的温度和保温时间可以调节析出纳米晶体的尺寸以及浓度，通常情况下热处理温度越高，保温时间越长，得到的纳米晶体尺寸越大，浓度越高。纳米晶体的析出使得玻璃在可见及近红外波段吸收明显增加，表现在玻璃的颜色发生明显的变化，并且随着纳米晶体尺寸的增加，玻璃的吸收增强，玻璃颜色变深。另一方面，纳米晶体的析出也使得玻璃的非线性光学性能得到了巨大的提高，三阶非线性极化率χ(3)达到10-8esu量级，比未析出纳米晶的玻璃提高了6个数量级，这主要归结为金属纳米晶体的表面等离子体共振效应和半导体纳米晶体的量子限域效应，并且随着析出纳米晶尺寸的增大和浓度的增高，玻璃的三阶光学非线性系数也随之增加，同时纳米晶体掺杂的玻璃还具有超快的光响应时间，约为300 fs，这些结果表明金属和半导体纳米晶体掺杂的玻璃在非线性光学器件上具有良好的应用前景。 2、在热处理成功析出各种纳米晶体的基础上，研究了高重复频率飞秒激光在玻璃中空间选择性诱导析出各种金属和半导体纳米晶体(如Si、Ge、Pb等)。聚焦的高重复频率飞秒激光的热累积效应产生的局域化高温场是纳米晶体三维可控析出的主要原因，并结合考虑界面球差效应后光场分布的理论模拟对飞秒激光诱导析出纳米晶体的显微结构进行了解释。研究了不同的激光参数对纳米晶体析出的影响，结果显示只有在合适的激光功率范围内，纳米晶体的析出才比较充分，另外长时间的激光辐照也能使晶体析出得更加充分。由于激光诱导析出的纳米晶体与玻璃基质的高折射率差值，可以利用这项技术制备光波导、高衍射效率的元件以及光子晶体等器件。同时激光诱导析出的纳米晶体也极大的增强了玻璃的三阶非线性光学性能，可以用来制备微光开关等非线性光学器件。 3、研究了低重复频率(1 kHz)和高重复频率(250 kHz)飞秒激光与硼硅酸盐玻璃相互作用时产生折射率变化的不同行为以及机理。1 kHz飞秒激光诱导玻璃产生的折射率变化较小，在10-4量级，而250 kHz飞秒激光诱导产生的折射率变化较大，在10-1量级。1 kHz飞秒激光与玻璃相互作用时产生了大量的SiE色心结构，但经过一定温度下热处理后可以使色心消失，同时玻璃经1 kHz飞秒激光辐照后微结构也发生了细微的变化，部分的[BO4]四面体中B-O键在飞秒激光作用下被打断了，从而形成了[BO3] 三角体，于是便导致[BO3] 三角体的增多和[BO4]四面体的减少。250 kHz辐照玻璃后结构产生了较大的变化，部分玻璃相在高重复频率飞秒激光热累积效应作用下析出纳米晶体，由于晶体和玻璃基质较大的折射率差，导致250 kHz飞秒激光诱导的折射率变化较大。另外还研究了不同温度热处理后玻璃的折射率变化，1 kHz飞秒激光诱导的折射率变化值随热处理温度的升高逐渐下降直至接近零，折射率差值变化的趋势与玻璃中色心浓度变化的趋势很吻合，表明折射率变化主要是由色心结构引起的，而250 kHz飞秒激光诱导的折射率变化值经热处理后基本没有变化，对应的激光诱导析出的纳米晶体的浓度也基本没有变化，表明折射率变化主要是析出的纳米晶体引起的。这个结果可用来快速制备各种以高折射率变化为基的光子学器件如光波导、耦合器、分波器、光栅等。 4、利用熔融热处理法制备了CdSe、CdTe、PbSe和PbTe量子点掺杂的硅酸盐玻璃。通过对热处理过程的控制可以调节量子点的尺寸大小以及尺寸分布，随着热处理温度的升高和热处理温度的增加，量子点的尺寸增大，量子点的尺寸分布先变宽后变窄，而随着量子点尺寸变大，量子点的吸收谱峰、吸收边和荧光峰表现出明显的红移现象，这是由量子尺寸效应引起的。另外，量子点掺杂玻璃的荧光发射可覆盖可见以及近红外1.1 μm -1.7 μm波段范围，并能通过控制量子点的尺寸大小以及尺寸分布来实现可调谐的宽带发光，在生物标记以及光通讯领域内有良好的应用前景。另一方面，量子点掺杂的玻璃表现出优异的三阶非线性光学性能，非线性吸收系数β可达到10-10 m/W量级，可有望应用于非线性光学器件比如全光开关。 5、利用250 kHz飞秒激光在硅酸盐玻璃中实现量子点的空间选择性析出。高重复频率的250 kHz飞秒激光的热累积效应产生的高温度场是量子点空间选择性析出的主要原因。结果表明只有在合适的飞秒激光功率范围(500 mW-800 mW)内量子点的析出才比较充分，另外通过调节激光功率、激光辐照时间或激光扫描速度等参数也可以控制析出量子点的尺寸大小和尺寸分布。飞秒激光诱导析出PbSe量子点也表现出在近红外1.1 μm -1.7 μm波段范围内可调谐的宽带的荧光性能和优异的非线性光学性能，同时由于飞秒激光诱导析出的PbSe量子点比玻璃基质的折射率高很多，我们也实现玻璃内部三维的高的折射率差值。这种飞秒激光诱导空间选择性析出量子点的技术在微型化、集成化和功能化的光学器件领域内具有良好的应用前景。
英文摘要	Femtosecond laser micro-/nanoprocessing technology has gained much attention over a large number of precision machining technologies, which is owing to its super resolution that can break through the optical diffraction limits, and capability of true three dimensional (3D) micro-/nanostructuring in transparent materials. It offers a good solution for realization of functional integrated, systemic miniature and structural adjustable devices. Remarkably, it has been widely used in the preparation of a variety of photonic devices, and it can provide a wealth of experimental and theoretical data for the development of fundamental sciences, such as high field physics, nonlinear optics, material science and so on. During the past two decades, people mainly concern 1 kHz femtosecond laser interaction with materials. However, in recent years, experiments as well as the physical mechanism of high repetition rate femtosecond laser - matter interaction have attracted widespread interests. Compared with the low repetition rate (1 kHz) femtosecond laser, the most significant feature of high repetition rate femtosecond laser (> 100 kHz) is the heat accumulation effect which can produce a localized high temperature field. Various heat-driven physical and chemical changes can be induced by the localized high temperature field inside the transparent materials, such as femtosecond laser induced 3D precipitation of a variety of optically functional crystals inside glasses. Although the research of laser induced crystallization was carried out earlier, the work was still not deep enough, and the kinds of precipitated crystals are also limited. In this thesis, space-selective precipitation of functional crystals induced by 250 kHz femtosecond laser has been studied systemic, various crystals have been precipitated successfully, including metal (Pb, Ga, and Cu), semiconductor (Si, Ge) nanocrystals and quantum dots (PbSe, PbTe, etc). We carried out the following researches: 1. We proposed a universal method to fabricate a variety of novel types of metal and semiconductor nanocrystals doped glasses and demonstrated their optical properties. Strong reducing agent is added to the glass raw materials, such as metallic Al, Zn and carbon powder, and then the metal or semiconductor oxides (for example SiO2) will be reduced to the atomic state (Si) by means of conventional glass melt-quenching processes. Upon subsequent heat-treatment, the atomic state of such metal and semiconductor elements will gather together, grow and form nanocrystal (such as Si, Ge, Pb, Bi and etc.) by atomic diffusion inside the glass. For comparison, we also prepared glass samples without metallic reducing agent Al but with Al2O3, however, nanocrystals can not be formed in such glasses, which indicate that the reducing agent plays a very important role in crystallization. Size and concentration of nanocrystals can be controlled by tuning the temperature and holding time of heat treatment process. In general, with higher heat treatment temperature and longer holding time, nanocrystals with larger average size and larger concentration can be obtained. The precipitation of metal and semiconductor nanocrystals increased the optical absorption in the visible and near-infrared region, showing a distinct change of glass color. Furthermore, the absorption of the glasses enhanced with the increase in the size of nanocrystals, On the other hand, the precipitation of the nanocrystals also greatly enhanced the third-order nonlinear properties of the glasses, the third-order nonlinear optical susceptibility χ(3) of nanocrystals doped glasses reaches up to 10-8 esu order of magnitude, which is 106 times larger than that of nanocrystals un-doped glass. This is mainly attributed to the surface plasma resonance effect of the metal nanocrystals and quantum confinement effect of semiconductor nanocrystals. The third-order optical nonlinearities increased with the increase of nanocrystal size and concentration, while the nanocrystals doped glasses also exhibit ultrafast optical response time (300 fs), these results show that the metal and semiconductor nanocrystals doped glass has a good application in the fabrication of nonlinear optical devices. 2. Space-selective precipitation of various metal and semiconductor nanocrystals (such as Si, Ge and Pb) induced by high repetition rate femtosecond laser in glasses has been studied on the basis of successful precipitation of nanocrystals in glasses by heat treatment. Localized high-temperature field generated from the heat accumulation effect of the focused high repetition rate femtosecond laser is the main reason for the three-dimensional precipitation of nanocrystals. Precipitation of nanocrystals by femtosecond laser irradiation has been explained by the theoretical simulation of optical field distribution after considering the effect of the spherical aberration. Influence of laser parameters on the precipitation of nanocrystals was analyzed. Results showed that nanocrystals will be precipitated fully only with appropriate laser power, while longer laser irradiation time will enable the precipitation of nanocrystals more fully. Since the high refractive index difference between the laser-precipitated nanocrystals and glass matrix, the precipitation of nanocrystals by femtosecond laser direct writing can be used for fabrication of photonic crystals and optical waveguide, diffraction devices with high efficiency. Furthermore, the laser precipitated nanocrystals greatly enhanced the nonlinear optical properties of glass, which can be used to the preparation of nonlinear optical devices such as optical switches. 3. Different refractive index change (RIC) phenomenon in borosilicate glass induced by low repetition rate (1 kHz) and high repetition rate (250 kHz) femtosecond laser has been analyzed. Smaller RIC (up to 10-4) was observed after 1 kHz fs laser irradiation, while larger RIC (up to 10-1) was detected after 250 kHz fs laser irradiation. A large number of SiE'' color centers were generated after 1 kHz femtosecond laser irradiation, but these color centers disappear after heat treatment. Meanwhile the glass microstructure was also changed a little after 1 kHz femtosecond laser irradiation, a part of B-O band in [BO4] tetrahedron was broke by laser pulse and forming of [BO3] triangle. On the other hand, giant structure change was observed after 250 kHz femtosecond laser irradiation, part of the glass phase was changed to crystal under the heat accumulation effort from the high repetition rate femtosecond laser. Large RIC obtained in the 250 kHz femtosecond laser induced glass was due to the large RIC between the precipitated crystal and glass matrix. Also, the influence of laser condition and annealing temperature on RIC was revealed. The value of RIC generated by 1 kHz femtosecond laser irradiation was gradually decreased until close to zero with the increase of heat treatment temperature, which consistent well with the decreasing trend of the concentration of SiE΄ color centers. However, the value of RIC generated by 250 kHz femtosecond laser irradiation was nearly unchanged, as well as the concentration of the laser precipitated nanocrystal. These results show that the RIC induced by 1 and 250 kHz femtosecond laser were ascribed to the formated color centers and precipited nanocrystals, respectively. This technique can be used to quickly preparation of a variety of photonic devices based on high refractive index change, such as optical waveguides, couplers, beam splitter, and gratings. 4. CdSe, CdTe, PbSe and PbTe quantum dot doped silicate glasses were prepared by the conventional melt-quenching process. Size and size distribution of quantum dots can be adjusted through the controlling of heat treatment process, the size was increased as the increase of temperature and holding time of the heat treatment, while the size distribution was firstly widened and then narrowed. With the increase of size of quantum dots, the absorption peak, absorption edge and fluorescence peaks of the quantum dots doped glasses showed a significant red shift behavior, which was due to the quantum size effect. The luminescence of the quantum dots doped glass covers visible and near-infrared (1.1-1.7 μm) region, and also can achieve a tunable broadband light-emitting by controlling the size and size distribution of quantum dots, which make them have potential application in the fields of biomarkers and optical communications. On the other hand, the quantum dots doped glasses showed excellent nonlinear optical properties, the nonlinear absorption coefficient β can reach up to 10-10 m/W, which can be applied to fabricate non-linear optical devices such as optical switches. 5. Space-selective precipitation of quantum dots was achieved in silicate glass by using 250 kHz femtosecond laser irradiation. High-temperature field generated from the heat accumulation effect of the focused high repetition rate femtosecond laser is the main reason for the 3D precipitation of quantum dots. The results showed that quantum dots will be precipitated fully only with appropriate laser power, meanwhile, the size and size distribution of the precipitation of quantum dots can be adjusted by turning the laser power, laser irradiation time and laser scanning speed. The laser precipitated PbSe quantum dot also shows tunable and broadband luminescence in the near-infrared region (1.1-1.7 μm) as well as excellent nonlinear optical properties. Furthermore, high-refractive index difference was also achieved by femtosecond laser micromachining which was ascribed to larger refractive index difference between PbSe and glass matrix. The femtosecond laser-induced space-selective precipitation of quantum dots technique has potential applications in the fields of miniaturized, integrated and functional optical devices.
语种	中文
内容类型	学位论文
源URL	[http://ir.siom.ac.cn/handle/181231/15702]
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	林耿. 飞秒激光在玻璃内部制备金属和半导体纳米晶体及其光学性能研究[D]. 中国科学院上海光学精密机械研究所. 2012.

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