【作者】 巫殷忠；

【导师】 王清月；

【作者基本信息】 天津大学 ， 光学工程， 2008， 博士

【摘要】 本论文主要研究利用飞秒激光对固体材料进行微细加工及其在微结构制作中的应用。1.讨论了飞秒激光在宽带隙透明固体电介质中诱导的多光子电离、隧道电离和碰撞电离过程,以及飞秒激光作用区域产生的局域等离子体密度随时间的变化。理论计算表明雪崩电离导致透明固体电介质破坏所需的时间很短,典型值为几十飞秒至百飞秒。另外讨论了飞秒激光在透明固体电介质内产生的自聚焦、等离子体自散焦及成丝现象等非线性光学效应引起的材料折射率改变。2.利用钛宝石飞秒激光放大器(中心波长775 nm、脉宽150 fs、重复频率1 kHz)作为写入光源,分别采用横向扫描模式和纵向扫描模式在熔融石英内直写制作光学波导。比较了横向扫描和纵向扫描两种直写模式的优缺点及各自直写的光波导的形貌,分析了横向扫描直写的光波导的横截面呈现椭圆形的原因,以及采用柱透镜或狭缝对入射光束预先整型的改善方法。实验讨论了飞秒激光的入射平均功率、扫描速度及重复扫描次数等参数对直写结果的影响,确定了直写良好性能光波导的条件,并用搭建的简易测试装置初步测试了直写的光波导的传输性能。3.利用近红外飞秒激光聚焦照射光敏玻璃FOTURAN,经热处理及在稀氢氟酸溶液中室温超声腐蚀,制作了竖直微孔、光滑微凹面及微通道等基础微结构。实验探索了飞秒激光入射参数对制作微结构形貌的影响,并确定了制作这些微结构的合适激光入射条件。实验发现飞秒激光曝光区域对激光入射参数(能流和脉冲数)的饱和效应,从充分反应消耗的角度对此进行解释。4.采用聚焦的近红外飞秒激光在光纤内逐点直写的方法,在未作增敏处理的光子晶体光纤和单模通信光纤内直接诱导了周期性结构改变。摸索了飞秒激光的入射平均功率及单点曝光时间对诱导结构改变的影响,为进一步利用近红外飞秒激光直写长周期光纤光栅提供指导。5.组建了一套基于掺镱(Yb)大模面积光子晶体光纤飞秒激光放大器的微纳加工系统,完善了该系统中三维微位移平台对刻划微图案的运动控制,通过氦氖光同轴监视的方法解决了加工时入射激光聚焦于样品表面的定位问题,并利用组建的加工系统对三类典型材料:半导体、金属薄膜和透明固体电介质进行了微纳加工实验。在硅片及金属薄膜(铬、铝)表面直接刻划方形和圆形等微图案的实验表明:刻划制作的微图案线条具有规整的边缘加工效果,且有效地减少了未加工区域受到的污染和热影响,从而保护了制作衬底。在具有高破坏阈值的熔融石英上的实验显示,若以比刻划硅片大得多的平均功率聚焦入射在其内部扫描,可以观察到激光聚焦点处的诱导成丝现象和伴随的可见光辐射。基于以上实验加工结果,分析了组建的飞秒激光加工系统的高重复频率和高平均功率特点为提高微纳加工效率及扩展材料加工能力所带来的优势。通过与典型的千赫兹重复频率的固体飞秒激光放大系统进行比较,阐述了基于光子晶体光纤飞秒激光放大技术的微纳加工系统在整体结构、环境稳定性及操作维护等方面的优点。更多还原

【Abstract】 Micromachining of solid materials employing near-infrared femtosecond laser and its application in fabricating microstructures is mainly studied in this dissertation.1. The multiphoton ionization, tunnelling ionization and collisional ionization induced inside wide-band-gap transparent bulk dielectrics by femtosecond laser are revealed, and evolution of the density of plasma localized in femtosecond laser-matter interaction area is discussed. Theorectical calculation shows that the time for avalanche ionization induced breakdown in transparent bulk dielectrics is very short, typically several tens to hundreds of femtosecond. The refractive-index-change induced by nonlinear optical effects producing in transparent bulk dielectrics by femtosecond laser, such as self-focusing, plasma defocusing and filamentation, are also discussed.2. Optical waveguide is directly written inside fused silica employing Ti: Sappire femtosecond laser amplifier (775 nm central wavelength, 150 fs pulse duration, 1 kHz repetition rate), by adopting transverse and longitudinal scanning modes, respectively. Merits and defects for two scanning modes (transverse and longitudinal) are both elucidated. The reason for elliptical cross-section of waveguides written by transverse scanning is analyzed and improvements of beam shaping beforehand by cylindrical lens or slit is proposed. The influences of incident average laser power, scanning velocity and iterative scanning times on writing results are experimentally investigated, and condition for writing optical waveguide with good performance is determined. A simple experimental setup is founded to characterize the written optical waveguide.3. Fundamental microstructures such as vertical micro-hole, smooth micro-concave surface and micro-channel are fabricated with a photosensitive glass (FOTURAN) employing focused irradiation of near-infrared femtosecond laser, followed by subsequent heat treatment and ultrasonic etching in dilute hydrofluoric acid solution at room temperature. Influences of incident femtosecond laser parameters on morphologies of fabricated microstructures are experimentally investigated, and appropriate condition for fabrication is determined. Saturation of dimensions of irradiated area with incident femtosecond laser paremeters (including fluence and number of pulse shots) is found during experiment, and it is explained based on fully reacting exhaustion.4. Employing focused near-infrared femtosecond laser direct writing, periodic structural change is induced inside non-sensitized photonic crystal fiber (PCF) and single mode communication fiber. Influences of incident average power and exposure time on the induced structural change are investigated, which facilitates the direct writing of long-period-fiber-grating by near-infrared femtosecond laser.5. Micromachining system based on Yb-doped large-mode-area photonic crystal fiber (PCF) femtosecond laser amplifier is founded. The motion control for fabricaiton of micro-pattern using three-dimensional translation stage in the system is improved and location of laser focus spot on the surface of a sample is solved by co-axial monitoring with helium-neon (He-Ne) laser. Three typical types of material, including semiconductor, metallic thin film and transparent bulk dielectrics, are micromachined by the founded system. Experimental results show that lines contained in the rectangular and circular micro-patterns directly written on the surface of silicon (Si), chromium (Cr) and aluminum (Al) film, own uniform and regular morphology. In addition, contamination and heat effect are effectively reduced during micromachining, which herein, protects the substrate. When femtosecond laser with much higher average power than that of direct writing on silicon is focused and scans inside fused silica, filamentation and concomitant visible radiation are found around the laser focus spot.Based on above experimental results, it is revealed that the characteristics of high repetition rate and high average power bring advantages of high efficiency and enhanced capability to the founded system in material processing. Comparing with typical solid kilohertz-repetition-rate femtosecond laser amplifier, the micromachining system based on PCF femtosecond laser amplifier exhibits merits in compact structure, environmental stability and manipulability.更多还原