飞秒激光对氟化镁烧蚀机理研究

用扫描电镜(SEM)研究了氟化镁在800nm超短脉冲激光作用下的单枪表面烧蚀形貌.根据烧蚀斑面积与激光脉冲能量间的对数关系，测得烧蚀阈值与激光脉宽的关系曲线(55—750fs).计算了导带电子的双光子吸收，改进了多速率方程模型，很好地解释了实验结果. 关键词： 飞秒激光 氟化镁 烧蚀机理 双光子吸收     

飞秒激光烧蚀硅表面产生等离子体的发射光谱研究

对中心波长为800 nm,脉宽为100 fs的激光脉冲烧蚀空气中硅(111)产生的等离子体发射光谱进行了时间和空间分辨研究. 结果表明,在等离子体羽膨胀初期(小于50 ns时间范围内),等离子体发射光谱主要由连续光谱构成,此后连续光谱强度逐渐减弱,线状光谱开始占主导地位;在羽体膨胀过程中离子谱线的存在时间短于原子谱线的存在时间. 由时间分辨发射光谱发现在羽体膨胀过程中等离子体辐射波长存在红移现象,波长红移量随时间演化呈二次指数衰减. 最后给出等离子体发射光谱谱线强度的时空演化规律. 关键词： 飞秒激光 脉冲激光烧蚀 等离子体 发射光谱     

多脉冲飞秒激光对锗材料的烧蚀效应

 开展了脉宽为40 fs的不同数量激光脉冲对锗材料的烧蚀效应实验,采用扫描电镜、激光共聚焦显微镜等方法对不同数量的飞秒激光脉冲作用下锗材料表面烧蚀区进行了检测,并对作用后材料烧蚀形貌演化规律进行了分析,初步分析了锗材料烧蚀区周围形成的不同环区的形貌特征及成因,对各环区烧蚀形貌特征随激光作用脉冲数的增加而产生的形貌演化过程进行了观测。并给出单脉冲飞秒激光对锗材料的烧蚀阈值为1.2 J·cm^-2,采用激光共聚焦显微镜测得该阈值条件下单个飞秒激光脉冲对锗材料的烧蚀深度约为150 nm。     

多脉冲飞秒激光对锗材料的烧蚀效应

开展了脉宽为40 fs的不同数量激光脉冲对锗材料的烧蚀效应实验,采用扫描电镜、激光共聚焦显微镜等方法对不同数量的飞秒激光脉冲作用下锗材料表面烧蚀区进行了检测,并对作用后材料烧蚀形貌演化规律进行了分析,初步分析了锗材料烧蚀区周围形成的不同环区的形貌特征及成因,对各环区烧蚀形貌特征随激光作用脉冲数的增加而产生的形貌演化过程进行了观测。并给出单脉冲飞秒激光对锗材料的烧蚀阈值为1.2 J·cm-2,采用激光共聚焦显微镜测得该阈值条件下单个飞秒激光脉冲对锗材料的烧蚀深度约为150 nm。     

飞秒激光烧蚀金属靶的冲击温度

在明确飞秒激光与物质相互作用过程冲击温度概念的基础上, 讨论了飞秒激光烧蚀铝靶和铜靶过程中的冲击温度与其他物理量的关系, 利用飞秒激光烧蚀金属的双温模型提取了冲击温度的绝对值, 基于非傅里叶热传导模型计算了冲击温度的分布. 此项研究结果对飞秒激光安全加工含能材料有借鉴意义. 关键词： 飞秒激光 含能材料 烧蚀 冲击温度     

单脉冲飞秒激光烧蚀炸药过程的热效应研究

飞秒激光能够在极短时间内烧蚀炸药产生高温高压等离子体。可以利用飞秒激光对含能材料或含能元器件进行精密加工。深入认识飞秒激光烧蚀炸药过程中,炸药内部的热效应是发展飞秒激光加工炸药技术的基础。建立了单脉冲飞秒激光烧蚀炸药过程的流固耦合计算模型,考虑了在高温高压等离子体和炸药自热反应的共同作用下,炸药内部的热效应。对飞秒激光烧蚀TNT炸药过程进行了流体力学数值模拟。计算结果表明：TNT炸药中未烧蚀区域产生了热效应,峰值温度高于TNT炸药的点火温度,但由于炸药内热效应区域极小,高温持续时间极短,因此炸药内温度迅速下降,没有发生点火现象。     

飞秒激光烧蚀氟化钙晶体表面特性

采用飞秒激光对氟化钙晶体表面进行加工。通过调控激光参数,采用静止聚焦和动态扫描两种方式在晶体表面加工出一系列微结构(烧蚀孔和烧蚀线)。分别对两种加工方式烧蚀后的氟化钙晶体表面微结构进行系统研究,包括参数依赖关系、材料表面烧蚀阈值等。计算结果表明:在静止聚焦情况下,累积因子为0.0033;在动态扫描情况下,当扫描方向与激光偏振方向垂直或平行时,累积因子分别为0.0043和0.0052。飞秒激光加工过程中的脉冲累积效应能够对晶体的烧蚀产生重要影响。     

制备水溶性CdS量子点的一种物理方法：飞秒激光烧蚀法

用Ti/sapphire飞秒激光系统产生的100fs、800nm激光对置于水中的CdS体相材料进行烧蚀,得到了水溶性CdS纳米粒子。这种纯物理过程保证了无污染的制备环境,从而保证了所合成材料的纯洁性。通过透射电子显微镜、紫外/可见/近红外吸收光谱、室温光致发光谱的方法对CdS量子点的形貌及其光学性质进行了表征。结果表明:利用飞秒激光烧蚀法所制备的CdS量子点可直接分散在水中而且具有粒径小、分布均匀的特点;同时具有较好的胶体稳定性,可在空气中稳定存放6个月以上。飞秒激光烧蚀法所制备的CdS量子点所具有的这些性质使其在生物标记领域引起极大的兴趣,而且也为纳米材料的制备提供了新的思路。     

基于飞秒激光的光纤切割加工工艺研究

为了得到理想的光纤切割断面,利用飞秒激光对石英光纤材料进行切割微加工实验。研究激光功率、脉冲频率、扫描速度等加工参数与光纤切割断面质量间的关系,以寻求最理想的加工参数。最后在可调倾角光纤夹具的辅助下,很好地弥补加工过程中产生的端面倾斜角,得到垂直度高达89.56°的光纤切割断面。     

飞秒激光烧蚀典型金属表面产生冲击波膨胀研究

利用时间分辨阴影成像技术进行飞秒激光烧蚀金属表面研究可以直观获取飞秒激光烧蚀金属表面产生冲击波膨胀过程的图像。通过对比飞秒激光烧蚀金属铝、铜、铁靶表面的冲击波膨胀形式发现:金属铜、铁表面的冲击波均以球面波形式传播;由于受到烧蚀物质喷溅的影响,铝靶表面竖直方向的冲击波传播形式由球面波转化为柱面波。     

Femtosecond laser near field ablation

The high field strength of femtosecond laser pulses leads to nonlinear effects during the interaction with condensed matter. One such effect is the ablation process, which can be initiated below the threshold of common thermal ablation if the excitation pulses are sufficiently short. This effect leads to structure formation, which is anisotropic because of the polarization properties of the near field and can result in pattern sizes below the resolution limit of light. These effects are explored by temporally resolved scattering methods and by post‐mortem analysis to show the non‐thermal and anisotropic nature of this process. The near‐field distribution of plasmon modes can be tailored to a large extent in order to obtain control of the pattern formation.     

飞秒激光精密微纳加工的研究进展

飞秒激光由于其超快时间特性和超高峰值功率特性在精密微纳加工领域引起了人们广泛的重视．在与物质的相互作用中它能快速、准确地将能量作用在特定的区域内，从而可以获得极高的分辨率和加工精度。文章综述了飞秒激光精密微纳加工的最新研究进展，分别就飞秒激光烧蚀微加工和飞秒激光双光子聚合产生三维微纳结构进行了介绍，阐述了各自的物理机制．最后对飞秒激光微纳加工的研究前景做了初步探讨。     

飞秒激光精密微纳加工的研究进展

飞秒激光由于其超快时间特性和超高峰值功率特性在精密微纳加工领域引起了人们广泛的重视.在与物质的相互作用中它能快速、准确地将能量作用在特定的区域内,从而可以获得极高的分辨率和加工精度.文章综述了飞秒激光精密微纳加工的最新研究进展,分别就飞秒激光烧蚀微加工和飞秒激光双光子聚合产生三维微纳结构进行了介绍,阐述了各自的物理机制.最后对飞秒激光微纳加工的研究前景做了初步探讨.     

Femtosecond laser ablation of DAST

High rate femtosecond (fs) laser ablation of the organic salt 4-N,N-dimethylamino-4-N-methyl-stilbazolium tosylate (DAST), an organic crystal with very high optical nonlinearities has been demonstrated. The threshold fluence and the ideal fluence range for damage free ablation for the wavelengths 550, 600, and 775 nm have been determined and the quality of the produced grooves has been investigated. The threshold fluences are in the order of 10–70 mJ/cm² and the ideal fluence range for damage free ablation is ranging from 30 to 300 mJ/cm², depending on the wavelength. The optimal focussing for ablation has been investigated and first results towards the structuring of a ridge waveguide are presented. We conclude that this method is most promising for waveguide patterning of DAST surfaces for integrated optics applications.     

飞秒激光在空气和水中对硅片烧蚀加工的实验研究

采用1 kHz,800 nm,50 fs—24 ps的钛宝石激光脉冲对单晶硅样品在空气和水溶液环境中的烧蚀加工特性进行了研究.实验观察到了超短脉冲激光在空气氛围中烧蚀形成的双层环状结构,分析揭示了加工区域中心和边缘的烧蚀物理机制分别为热熔化和库仑爆炸,并测量了双层环状结构半径随入射激光能量、脉冲数及持续时间等的变化关系,结果表明获取较大深-宽比的加工效果需选择小能量脉冲激光的多次作用.在水溶液环境中,实验发现飞秒激光在样品表面诱导产生了亚微米量级的多孔状结构,而皮秒激光则更容易实现对硅表面的非热性去除.这是由于激光诱导的光机械应力和空泡效应随脉冲宽度变大而增强所致,在实验上确立了区分这两种不同加工状态的临界脉冲宽度. 关键词： 飞秒激光 硅片 激光加工     

Femtosecond pulsed laser ablation with spatial filtering

With the rise in demand for miniaturized features with better acute edge acuity and negligible thermal damage zone, one of the key vital areas lies in the refinement of the quality of the laser beam itself. Spatial filter is routinely used in optical micromachining systems to smoothen the Gaussian profile of the machining spot in order to obtain a feature of the desired quality. However, its profile smoothening effect has never been investigated for femtosecond pulsed laser micromachining process since the extremely high peak power of femtosecond pulses will cause damage on the filtering aperture of spatial filter. During the development of an acousto-optical micromachining system using femtosecond pulses, we found that if the damage of the filtering aperture can be circumvented, spatial filter can improve the machining quality of femtosecond pulse ablation, especially when ablation is conducted at low-fluency range (just above the ablation threshold fluency). In this paper, we investigate and demonstrate both the improvement and potential that beam refinement can bring about. In our experiment, a series of test patterns were ablated with a 400 nm second-harmonic Ti:Sapphire femtosecond laser of 150 fs duration at varying pulse energy ranging from 31 to 39 nJ. The specimen used in the experiment is a platinum- (Pt) sputtered coating of 100 nm thickness on a quartz substrate. The results show a significant improvement in the constancy of the shape as well as the size of ablated feature, revealing an improved beam profile and beam energy distribution due to spatial filtering.     

Femtosecond pulsed laser ablation of thin gold film

Laser micromachining on 1000 nm-thick gold film using femtosecond laser has been studied. The laser pulses that are used for this study are 400 nm in central wavelength, 150 fs in pulse duration, and the repetition rate is 1 kHz. Plano-concave lens with a focal length of 19 mm focuses the laser beam into a spot of 3 μm (1/e² diameter). The sample was translated at a linear speed of 400 μm/s during machining. Grooves were cut on gold thin film with laser pulses of various energies. The ablation depths were measured and plotted. There are two ablation regimes. In the first regime, the cutting is very shallow and the edges are free of molten material. While in the second regime, molten material appears and the cutting edges are contaminated. The results suggest that clean and precise microstructuring can be achieved with femtosecond pulsed laser by controlling the pulse energy in the first ablation regime.     

飞秒脉冲烧蚀单晶硅的超快动力学

利用基于Pump-probe系统的超快时间分辨阴影图的方法,研究了空气中飞秒激光烧蚀单晶硅的动力学过程。实验采用脉宽为50 fs、平均能量密度约35 J/cm2的单脉冲激光烧蚀单晶硅,获取飞秒激光烧蚀单晶硅过程中等离子体和冲击波的形成和发展过程的时间分辨阴影图。实验结果表明：飞秒激光烧蚀单晶硅导致其表面物质喷发的过程是不连续的,分为明显的两次喷发过程。这表明飞秒激光与单晶硅作用的过程中,在不同的时间段可能由不同的机制主导,在前期可能是多光子电离为主,在后期可能是由多光子效应和雪崩效应共同作用。研究还发现,延迟时间较长时,冲击波形状发生畸变。     

金掺杂PMP泡沫的制备与表征

以聚-4-甲基-1-戊烯(PMP)为泡沫骨架材料,金颗粒为掺杂材料,均四甲苯与萘为混合溶剂体系,通过热诱导倒相技术制备出金掺杂低密度聚合物泡沫。实验结果表明：在金含量不变的情况下,掺杂泡沫的实际密度与理论密度呈线性关系;在理论密度不变的情况下,掺杂泡沫的实际密度随掺杂质量分数的增加趋近于理论值;金实际掺杂质量分数低于理论掺杂质量分数;掺杂泡沫与纯PMP泡沫具有类似的孔洞结构,随掺杂质量分数的增加泡沫的孔洞直径分布变宽且网络骨架尺寸有变大的趋势。