超短脉冲激光烧蚀绝缘体材料机理的耦合理论模型

基于电子能带理论,以动力论的Fokker_Planck方程为基础,从微观层次对超短脉冲激光烧蚀绝缘体材料的机理进行分析研究.源项中分别考虑了雪崩电离、多光子电离机制,并考虑了电子能量与散射机制对电子弛豫时间的影响.建立了绝缘体烧蚀机理的耦合数学模型,其计算的激光烧蚀临界能量密度阀值与实验结果很好的吻合.定量描述了超短脉冲激光对绝缘体材料烧蚀微观过程的影响.     

超短脉冲激光对岩石的烧蚀作用研究

对干燥状态和浸水后的红砂岩、花岗岩、大理岩在不同超短脉冲激光入射频率和烧蚀发次等条件下的烧蚀情况进行了研究.结果发现,浸水后的岩石烧蚀质量损失明显大于干燥状态下的质量损失.同时质量损失与激光入射频率和烧蚀发次有着密切的关系.     

超短强激光脉冲在大气传播中的自聚焦行为

通过建立涉及克尔效应和多光子电离效应的非线性数学模型,利用数值方法研究了超短激光脉冲在大气传播中的聚焦行为。结果表明由自聚焦导致的成丝现象具有间断,而不是一种稳态的模式。每次轴上的成丝都会由于光场损耗减弱,但同时由于克尔效应会使离轴区域的能量间断地补充到光轴上。     

时空分布的超短激光脉冲烧蚀电介质材料时等离子体的产生

若考虑聚焦平面内固定区域,脉冲空间分布可简化为一维问题.在此基础上,从脉冲的传输过程出发,本文分析了时空分布的超短激光脉冲与电介质材料相互作用时等离子体形成模式.在材料内部累积的能量与脉冲宽度、与空间相关的损伤区域、等离子体形成时间及其吸收系数有关.     

超短脉冲激光烧蚀石墨产生的喷射物的时间分辨发射光谱研究

本文使用不同激光能流(18 J/cm²–115 J/cm²)和脉冲宽度(50 fs–4 ps)的超短脉冲激光在真空中(4×10^-4 Pa)烧蚀高定向热解石墨. 通过测量烧蚀喷射物的时间分辨发射光谱研究喷射物的超快时间演化. 在喷射物发射光谱中, 观察到了C₂基团的天鹅带光谱系统, 416 nm附近C₁₅基团的由电子能级¹Σ_u⁺ 和¹Σ_g⁺之间的振动跃迁产生的光谱峰以及连续谱. 50 fs, 115 J/cm²的脉冲激光烧蚀产生的喷射物的连续谱的强度衰减分为快速下降和慢速下降两个阶段(以20 ns时间延迟为分界). 这表明连续谱是由两种不同的组分贡献的. 快速下降阶段, 连续谱主要由碳等离子体通过韧致辐射产生; 慢速下降阶段, 连续谱主要由烧蚀后期产生的大颗粒碳簇的热辐射贡献. 实验结果还揭示了激光能流的提高, 会明显增加喷射物中碳等离子体和激发态C₂的含量, 但对质量稍大的C₁₅的影响较小; 此外, 50 fs脉冲激光烧蚀产生的连续谱的存在时间会随着激光能流的减小而增大, 这说明低能流更有利于在烧蚀后期产生碳簇. 脉宽主要影响喷射物连续谱的时间演化. 4 ps脉冲激光烧蚀产生的连续谱的整个时间演化过程明显慢于50 fs脉冲产生的连续谱.     

脉冲激光制备薄膜材料的烧蚀机理

研究了脉冲激光烧蚀靶材的整个过程.从包含热源项的导热方程出发，利用适当的动态边界条件，详细研究了靶材在熔融前后的温度分布规律，并且给出了熔融后的固、液分界面的变化规律.熔融后的温度演化规律和固液相界面均以解析表达式的形式给出.还根据能量平衡原理给出烧蚀面位置随时间的变化规律.以硅靶材为例计算模拟了激光烧蚀的整个过程，与实验结果符合较好. 关键词： 脉冲激光 烧蚀面 熔融 温度演化     

超短强激光脉冲激励甲烷团簇的内电离机理

采用三维粒子动力学模拟方法研究了甲烷团簇在超短强激光脉冲激励下的爆炸动力学行为,重点讨论了几种典型的内电离机理对团簇爆炸过程中离子的价态和动能的影响.研究表明,在激光脉冲强度比较小的情况下,团簇中的原子主要是在光场作用下通过隧道电离的方式发生电离.当激光场进一步增强时,势垒压低电离是电离的主要方式.在相同的较高激光强度下,团簇更容易通过势垒压低电离达到高的电离价态.团簇发生电离后,其内部库仑电场的点火电离效应和内部滞留自由电子的碰撞电离效应也将增强团簇的再次电离过程. 关键词： 超短强激光脉冲 甲烷团簇 内电离     

超短脉冲激光照射下氧化铝的烧蚀机理

利用烧蚀面积与激光脉冲能量的线性关系，确定了氧化铝的破坏阈值，同时采用散射光探测法，研究了800和400nm超短脉冲激光作用下氧化铝的破坏阈值对激光脉宽的依赖关系，并探讨了氧化铝的烧蚀规律. 利用雪崩击穿模型，解释了实验结果，并讨论了导带电子光吸收机理. 关键词： 飞秒激光 氧化铝 破坏阈值 雪崩模型     

对超短脉冲激光引雷产生的等离子体通道的特性分析

利用隧道电离诱导闪电模型,对超短脉冲激光在大气中产生弱等离子体通道的电阻和阈值强度进行了分析和计算。结果显示：强度为1014 W/cm2量级的超短脉冲激光产生的气体等离子体通道有较好的导电性,所需激光能量很小, 说明在该模型下激光能量的利用效率很高。     

对超短脉冲激光引雷产生的等离子体通道的特性分析

 利用隧道电离诱导闪电模型,对超短脉冲激光在大气中产生弱等离子体通道的电阻和阈值强度进行了分析和计算。结果显示：强度为10¹⁴ W/cm²量级的超短脉冲激光产生的气体等离子体通道有较好的导电性,所需激光能量很小, 说明在该模型下激光能量的利用效率很高。     

非线性附加耦合腔产生超短激光脉冲

系统地研究了用带有非线性倍频晶体的附加耦合腔来压窄激光光脉冲的动力学作用过程，首次给出了该锁模激光系统在瞬态平衡时输出脉宽的具体表达式，实验测量结果与理论计算值相比吻合得很好；最后，文中还报道了有关实验参量与该锁模激光系统输出特性的关系曲线。     

A New Synthetical Model of High-Power Pulsed Laser Ablation

We develop a new synthetical model of high-power pulsed laser ablation, which considers the dynamic absorptance, vaporization, and plasma shielding. And the corresponding heat conduction equations with the initial and boundary conditions are given. The numerical solutions are obtained under the reasonable technical parameter conditions by taking YBa2CusO7 target for example. The space-dependence and time-dependence of temperature in target at a certain laser fluence are presented, then, the transmitted intensity through plasma plume, space-dependence of temperature and ablation rate for different laser fluences are significantly analyzed. As a result, the satisfactorily good agreement between our numerical results and experimental results indicates that the influences of the dynamic absorptance, vaporization, and plasma shielding cannot be neglected. Taking all the three mechanisms above simultaneously into account for the first time, we cause the present model to be more practical.     

A New Synthetical Model of High-Power Pulsed Laser Ablation

We develop a new synthetical model of high-power pulsed laser ablation, which considers the dynamic absorptance, vaporization, and plasma shielding. And the corresponding heat conduction equations with the initial and boundary conditions are given. The numerical solutions are obtained under the reasonable technical parameter conditions by taking YBa₂Cu₃O₇ target for example. The space-dependence and time-dependence of temperature in target at a certain laser fluence are presented, then, the transmitted intensity through plasma plume, space-dependence of temperature and ablation rate for different laser fluences are significantly analyzed. As a result, the satisfactorily good agreement between our numerical results and experimental results indicates that the influences of the dynamic absorptance, vaporization, and plasma shielding cannot be neglected. Taking all the three mechanisms above simultaneously into account for the first time, we cause the present model to be more practical.     

Silicon Ablation by Single Ultrashort Laser Pulses of Variable Width in Air and Water

The ablation of silicon by single laser pulses of variable width (0.3–9.5 ps) with a wavelength of 515 nm has been comparatively studied in air and water. A nonmonotonic behavior of ablation thresholds with a minimum at 1.6 ps, which is due to achieving the thermalization time of the electron and ion subsystems in silicon, has been revealed. It has been shown that, with an increase in the pulse width in the considered width range, the efficiency of the ablation of silicon decreases by a factor of 2.5 in air and increases by a factor of 2 in water. This behavior of ablation in air is attributed to a partial transition from phase explosion to surface evaporation, which is suppressed in water.     

Non-Thermal Laser Ablation Model for Micro-Surgical Applications

We have developed a non-thermal laser ablation model which may reduce thermal damage to neighboring structures. Based on this model, the three critical parameters for a well controlled non-thermal microsurgery are (1) the laser wavelength with its photon energy matching closely the bond dissociation energy, (2) the energy fluence must be above threshold to avoid thermal process due to non-radiative relaxation from the excited electronic states to vibrational, (3) ultra short laser pulses (few fs) to completely eliminate thermal and direct biomolecular reactions. In this model the UV laser photon dissociates the molecular bonds which leads to the splitting of longer polymer chains into small fragments. The excess energy if any may appear as kinetic energy in the polymer-fragments. The extreme rapidity of the bond breaking process reduces heat conduction. The model establishes a relationship between ablation depth per pulse, the absorption coefficient, the incident laser energy fluence, and the threshold energy fluence. The ablation depths per pulse were calculated for the polymers Polymethyl methacrylate (PMMA) and polyimide for various commercially available UV lasers. It has been found that the minimum ablations depth occurs at 193 nm for both PMMA and polyimide. This assures a well defined incision with minimal thermal damage to the surrounding structures at this wavelength. There exists a definite threshold energy fluence for non-thermal ablation for any given biomolecule and below the threshold the non-radiative relaxation process may cause thermal ablation. New ultra fast lasers (few femtoseconds) (fs) will completely eliminate thermal diffusion as well as direct biomolecular reactions.     

Laser Ablation Inductively Coupled Plasma Mass Spectrometry: Principles and Applications

Abstract

The application of laser ablation inductively plasma mass spectrometry (LA‐ICP‐MS) to the determination of major, minor, and trace elements as well as isotope‐ratio measurements offers superior technology for direct solid sampling in analytical chemistry. The advantages of LA‐ICP‐MS include direct analysis of solids; no chemical dissolution is necessary, reduced risk of contamination, analysis of small sample mass, and determination of spatial distributions of elemental compositions. This review aims to summarize recent research to apply LA‐ICP‐MS, primarily in the field of environmental chemistry. Experimental systems, fractionation, calibration procedures, figures of merit, and new applications are discussed. Selected applications highlighting LA‐ICP‐MS are presented.     

10μm超短脉冲激光系统

具有新颖表面电晕预电离单模ＴＥＡＣＯ２激光器，等离子体开关和热吸池的光学自由诱导衰变（ＯＦＩＤ）激光系统产生３０－３００ｐｓ１０．６μｍ激光。     

ICP光源的激光烧蚀固体样品引入方法进展

根据近几年来国内外的有关文献,叙述了ICP光源的激光烧蚀固体进样方法的研究进展及其在物质成分分析中的应用。着重阐述了激光输出特性(输出波长、脉冲宽度、重复频率、能量密度)和环境气氛(氦气、氩气)对样品烧蚀过程的影响,讨论了激光烧蚀室、气溶胶传输管道及样品引入改进装置在蒸发物质被传输到ICP光源过程中的作用。获得较小而均匀的气溶胶颗粒和稳定高效地将烧蚀物质输送到ICP是完善激光烧蚀固体进样技术的关键环节,元素分馏效应及蒸发物沉积是影响分析性能的重要因素。作为实际例子,也讨论了激光烧蚀固体进样电感耦合等离子体发射光谱法/质谱法在金属、玻璃、有机物及其他样品分析方面的应用,对分析方法的准确度、精密度、检出限和灵敏度进行了简要论述。