脉冲激光烧蚀块状靶材的双动态界面研究

给出脉冲激光作用块状靶材的烧蚀模型.根据能量平衡原理,导出烧蚀面的位置随时间的变化关系.利用绝热近似、温度连续性条件和能量平衡原理来获得烧蚀面与固液相界面边界条件.结合热传导方程,利用精确解与积分近似法相结合的方案,给出固液两相的温度分布与时间和位置的变化关系,以及固液相界面的位置随时间的变化规律,并与已有的理论和实验结果进行比较.最后以铝靶为例计算模拟了激光烧蚀的全过程计算. 关键词： 脉冲激光 等离子体 固液相界面 烧蚀面     

脉冲激光烧蚀材料等离子体反冲压力物理模型研究与应用

分析了脉冲激光烧蚀材料等离子体等温膨胀阶段的物理特性,建立了脉冲激光烧蚀材料等离子体压力三维方程与动力学模型.应用所建模型,数值分析了单脉冲激光烧蚀青铜金刚石砂轮等离子体相关特性,得到等离子体的反冲压力最大值870 Pa出现在约25 ns后,距离砂轮表面距离约0.05 mm处.相关条件下开展脉冲激光烧蚀青铜金刚石砂轮试验,采用高速相机观测烧蚀砂轮过程中的飞溅现象;采用光栅光谱仪测量等离子体空间发射光谱,计算了等离子体电子温度、电子密度以及反冲压力.实验表明脉冲激光烧蚀青铜金刚石砂轮等离子体反冲压力可以不计,同时也验证了气体方程与动力学模型的正确性和可行性,对脉冲光纤激光烧蚀工艺优化具有启示意义.     

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     

纳秒脉冲激光沉积薄膜过程中的烧蚀特性研究

研究了高能短脉冲激光薄膜制备的整个烧蚀过程.首先建立了基于超热理论的烧蚀模型，然 后利用较为符合实际的高斯分布表示脉冲激光输入能量密度，给出了考虑蒸发效应不同阶段 的烧蚀状态方程.结合适当的边界条件，以Si靶材为例，利用有限差分法得到了靶材在各个 阶段温度随时间和烧蚀深度的演化分布规律及表面蒸发速度与烧蚀深度在不同激光辐照强度 下随时间的演化规律.结果表明，在脉冲激光辐照阶段，靶材表面的蒸发效应使得靶材表面 温度上升显著放缓；在激光辐照强度接近相爆炸能量阈值时，蒸发速度与蒸发厚度的变化由 于逆流现象将显著放缓.还得到了考虑了熔融弛豫时间及蒸发效应的固-液界面随时间的演化 方程，这一结论较先前工作更具有普适性. 关键词： 脉冲激光烧蚀 热流方程 温度演化 有限差分法     

飞秒激光诱导锗等离子体辐射光谱特性

由于飞秒激光脉冲宽度小于靶材电子—晶格热弛豫时间,飞秒激光烧蚀靶材过程以及诱导击穿产生的等离子体膨胀动力学过程与纳秒激光作用过程不同,因此研究飞秒激光诱导等离子体发射光谱特性对于研究飞秒激光烧蚀机制以及飞秒激光诱导等离子体的膨胀动力学过程非常重要。Ge材料是一种常用的中远红外探测器以及光学元器件材料,对中心波长为800 nm,脉宽为50 fs的激光脉冲烧蚀空气中Ge靶材产生的等离子体发射光谱强度的时间和空间演化规律研究,并探讨了飞秒激光脉冲能量对等离子体发射光谱强度的影响规律。实验结果表明在等离子体羽膨胀初期,飞秒激光诱导Ge等离子体发射光谱主要由线状光谱和连续光谱构成,在200 ns时间内连续光谱强度逐渐减弱,线状光谱开始占主导地位。通过探测Ge等离子体的时间分辨发射光谱,随着等离子体的快速膨胀,等离子体发射光谱强度随着时间的增加呈现先增加后下降变化,在335 ns达到最大。通过探测Ge等离子体的空间分辨发射光谱,随着距离Ge靶材表面的位置增加,等离子体发射光谱强度随远离Ge靶材表面距离增加呈现先增加后下降变化,在0.8 mm位置达到最大。由于存在等离子体自吸收机制,等离子体发射光谱...     

飞秒双脉冲激光照射金属薄膜的热行为

通过双温方程对飞秒单脉冲与双脉冲照射金薄膜进行了计算模拟分析,得到了金靶的电子温度和晶格温度随着时间空间的变化。在同样激光能量密度下,单脉冲与双脉冲使得金膜温度的变化表明双脉冲使得更多的激光能量渗透到靶材内部,这些能量可以使得烧蚀深度更深,有利于提高激光烧蚀靶材的效率。计算结果显示随着激光能量密度的增加熔化面深度逐渐增加,单脉冲与双脉冲熔化面深度的变化明显不同。在激光能量密度高于损伤阈值附近,单脉冲的烧蚀深度大于双脉冲的烧蚀深度,随着激光能量密度增加,双脉冲的烧蚀深度将大于单脉冲的烧蚀深度。     

飞秒多脉冲激光烧蚀金属过程中的能量剩余现象

 提出了描述整个飞秒多脉冲激光烧蚀过程的物理模型,模型考虑了多脉冲烧蚀的新的特点,考虑靶材吸收率随温度的变化和蒸发效应,建立了激光烧蚀不同阶段的热传导方程,给出了相应的定解条件。以金靶材为例,利用有限差分法,求解了热传导动力学方程,分别给出单脉冲和多脉冲作用下相应的靶材电子和离子亚系统的温度演化图像,及多脉冲激光作用下能量剩余系数和脉冲个数的变化规律,发现理论曲线与相应的实验数据吻合较好。研究结果充分证明多脉冲激光烧蚀过程中剩余能量的存在。     

靶材吸收率变化与烧蚀过程熔融前靶材温度分布

讨论了脉冲激光沉积法中烧蚀阶段熔融前靶材吸收率的变化对于其温度分布的影响. 给出了靶材吸收率随时间的变化规律，并在此基础上，利用较为符合实际的高斯分布表示脉冲激光输入能量密度，建立了相应的热传导方程. 结合适当的边界条件，利用有限差分法，以硅靶材和钨靶材为例，给出了靶材熔融前温度分布随时间和深度变化的演化分布规律，同时对相关过程的物理图像进行详细的讨论.对于吸收率的变化与脉冲激光能量密度的分布对于相应过程的影响，进行了分析讨论. 结果表明，在脉冲激光中间的持续过程中，忽略靶材吸收率的变化对于最终的模拟结果有重要影响，从而导致理论结果与实验数据有较大差异. 关键词： 脉冲激光沉积 吸收率 有限差分 温度演化     

甘油的黏度对激光等离子体推进的影响

以液体甘油为烧蚀靶材,研究了不同环境温度下超短脉冲激光烧蚀后产生的等离子体的推进特性.实验结果表明:甘油产生的动量和烧蚀压力与环境温度密切相关,其原因是甘油的黏度受温度影响较大.     

热阻塞效应对激光辐照靶材烧蚀过程的影响分析

研究了百兆瓦级激光烧蚀碳/碳复合材料靶材产生的等离子体吸收激光束能量引起的热阻塞效应。首先,基于逆轫致吸收理论,建立了激光在烧蚀靶材产生的等离子体中的传播模型;然后,基于磁流体理论,得到了等离子体在百兆瓦级激光形成的电磁场中的波动方程,建立了等离子体吸收激光能量引起热阻塞效应的模型。最后,对烧蚀过程中粒子的总密度、吸收系数、靶材表面等效热流随激光持续时间的变化规律以及是否考虑热阻塞效应时,靶面垂直方向的温度场进行了数值模拟。结果表明:等离子体的形成,对激光形成了明显的热阻塞效应,削弱了激光对靶材的烧蚀作用,使粒子总密度、吸收系数、靶材表面等效热流以及靶面垂直方向温度场的变化均呈现为非线性。     

基于激发态吸收的C60分子全光开关特性研究

用５３２．０ｎｍ的脉冲Ｎｄ：ＹＡＧ激光作为泵浦光，７４７．０ｎｍ的连续半导体激光作为探测光，在Ｃ₆₀甲苯溶液中，利用Ｃ₆₀分子的三重态－三重态非线性吸收效应，获得Ｃ₆₀分子的全光开关和全光调制特性，并用速率方程进行了动力学数值模拟，得到与实验相一致的结果。 关键词：     

Emission properties of laser ablation of SnO2: Sb transparent conducting film and KTiOPO4 crystal

Optical emission spectra of Nd:YAG laser ablation of KTiOPO₄ (KTP) crystal and SnO₂:Sb transparent conducting thin film were recorded and analyzed in vacuum and in air. The integral intensities of spectral lines from laser-ablated KTP crystal were obtained as functions of distance from the target surface and laser power density in vacuum and in air. The ambient gas effects on pulsed laser ablation of target were discussed. We also performed laser ablation of SnO₂:Sb transparent conducting thin film in air and the electron temperature and full-width at half-maximum (FWHM) of atomic and ionic spectral lines in the plasma were quantified using Boltzmann plot method and Lorentzian fit, respectively. Integral intensities of atomic and ionic Sn spectral lines were also obtained as functions of distance from the target surface and laser irradiance. The intensity ratio of ionic and atomic Sn spectral lines as a function of laser power density was got which gives some information about the variation of ionization ratio with laser irradiance in the plasma produced by high-power laser.     

激光频带宽度对二次谐波时空分辨结构的影响

本文报道用条纹相机在沿与激光光轴成90°方向拍摄的二次谐波发射的时空分辨结构,宽频带激光打靶与窄频带激光打靶表现出明显的差异,用孤立波产生理论进行分析,得出与实验基本相符的结果。 关键词：     

Pulsed laser ablation of solids: transition from normal vaporization to phase explosion

We present experimental data on mass removal during 1064-nm pulsed laser ablation of graphite, niobium and YBa₂Cu₃O_7-δ superconductor. Evidence for the transition from normal vaporization to phase explosion has been obtained for these materials, showing a dramatic increase in the ablation rate at the threshold fluences of 22, 15 and 17.5 J/cm², respectively. A numerical model is used to evaluate the ablation rate and temperature distribution within the targets under near-threshold ablation conditions. The results are analyzed from the viewpoint of the vaporized matter approaching the critical point with increasing laser fluence. A possible means of the estimating the thermodynamic critical temperature from the data for nanosecond laser ablation is discussed. It is suggested that the critical temperature of refractory metals is higher than that estimated with the traditional methods due to plasma effects. An analogy with the boiling crisis (the transition from nucleate to film boiling) is drawn to explain the formation of ablation craters with spallated edges. Received: 18 May 2000 / Accepted: 14 July 2000 / Published online: 22 November 2000     

Effect of oxygen injection on the size and compositional evolution of ZnO/Zn(OH)<Subscript>2</Subscript> nanocomposite synthesized by pulsed laser ablation in distilled water

Zinc oxide/hydroxide nanocomposite materials are synthesized by pulsed laser ablation of zinc in double distilled water. Effect of simultaneous flow of oxygen in the closed vicinity of laser ablated plasma plume on the size, morphology, crystallinity, and composition of synthesized oxide/hydroxide nanocomposite structures is investigated. As synthesized nanocomposite materials are characterized using UV–visible absorption, Scanning electron microscopy (SEM), thermo gravimetric analysis (TGA), Differential thermal analysis (DTA), X-ray diffraction (XRD), Fourier transform infrared (FTIR), and photoluminescence spectroscopic methods. It is observed that injection of oxygen induces a new mechanism in the particle synthesis, which causes decrease in particle size, distribution as well as Zn(OH)₂/ZnO ratio and increase of order of crystallinity of product. There are some novel findings in the direction of development of pulsed laser ablation in aqueous media (PLAAM) for the synthesis of nanostructured materials.     

Synthesis and characterization of TiOx nanoparticles prepared by pulsed-laser ablation of Ti target in water

Nanoparticles (NPs) creation by pulsed-laser ablation of targets in a liquid environment has recently become a promising technique, which has several relative advantages, such as simplicity and low cost. This technique was employed in the present work for preparation of TiO_x NPs suspension by ablation of metal Ti targets into twice-distilled water. A second harmonic generation (SHG) pulsed Nd:YAG laser was used in the experiments. Preferential formation of spherical NPs and their TiO_x nature was established. Aggregation of the created particles during aging was found. Transition of the NPs’ structure from amorphous to crystalline with increasing the laser energy was revealed. A difference was observed in the transmittance of the suspensions obtained depending on the laser intensity.     

SiH4激光等离子体内自由基反应动力学研究

本工作采用时间分辨的OES(Optics Emission Spectroscopy)技术,研究横向激励大气压(TEA)CO₂激光诱发的SiH₄等离子体内碎片反应动力学过程。实验结果表明,等离子体内某些碎片的发光特征谱线主峰位置明显不同。据此,讨论了各碎片的产生及反应过程。比较各碎片发光的持续时间及综合其它OES结果,我们认为SIH₄激光等离子体的最终反应通道为产生Si的通道。 关键词：     

Thermal model for nanosecond laser sputtering at high fluences

The vaporization effect and the following plasma shielding generated by high-power nanosecond pulsed laser ablation are studied in detail based on the heat flux equation. As an example of Si target, we obtain the time evolution of the calculated surface temperature, ablation rate and ablation depth by solving the heat flow equations using a finite difference method. It can be seen that plasma shielding plays a more important role in the ablation process with time. At the same time, the variation of ablation depth per pulse with laser fluence is performed. Our numerical results are more agreed with the experiment datum than other simulated results. The result shows that the plasma shielding is very important.     

Dispersion of zirconium dioxide by pulsed laser radiation

A technique for producing ZrO₂ dioxide nanoparticles under the action of pulsed laser radiation is developed. By the methods of transmission electron microscopy and X-ray phase analysis, it is shown that the high-temperature cubic phase of ZrO₂ is formed during laser ablation. The dependence of the size of ZrO₂ dispersed particles on the laser radiation intensity is determined. A thermodynamic one-dimensional model of laser ablation of zirconium dioxide is analyzed. The results of analytical computations of ablation of ZrO₂ particles are confirmed by experimental data.