共查询到19条相似文献,搜索用时 312 毫秒
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超短脉冲激光加热可应用于研究材料中载能子之间的超快相互作用,同时也广泛应用于超快激光加工.此前人们提出的双温度模型和抛物一步模型都只能用于描述超短脉冲激光加热金属薄膜后热量传递过程的特定片段.基于双温度模型和傅里叶导热定律,提出普适的理论模型可用于完整描述飞秒激光加热金属薄膜/基底时的整个热量传递过程.同时在300 K温度下,采用背面抽运-表面探测瞬态热反射法实验研究了飞秒脉冲激光加热金属薄膜的热量传递过程,理论预测曲线和实验测量结果符合较好,验证了理论模型的正确性.基于此模型测量得到了金薄膜的电子-声子
关键词:
飞秒脉冲激光
电子-声子耦合
界面热导
瞬态热反射 相似文献
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为研究双温方程中电子热传导项和电子与晶格耦合项对激光辐照物体表面温度场求解的影响,对这两项施加了约束条件。由于飞秒和亚皮秒激光与物质相互作用时间短,电子与晶格来不及耦合,所以对耦合项施加时间约束;根据相分离条件(CPPS),对热传导项施加空间约束。利用有限元方法建立了激光烧蚀金属铜膜表面的有限元模型。通过分析双温方程中热传导项和耦合项对计算结果的影响,发现短脉冲激光与铜金属相互作用过程中电子与晶格耦合项可以忽略,而传导项不可忽略。求解适当激光功率下的双温方程,得到了激光作用中心电子与晶格在不同脉冲宽度激光辐照下的温度变化关系。根据100 fs激光作用后晶格温度场的空间分布情况,研究了激光作用的相分离区域、相爆炸区域以及熔融区域的分布情况。 相似文献
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利用双曲-双温两步热传导和热电子崩力模型,考虑到晶格温度与应变速率的耦合效应,得到了用于描述飞秒激光作用下金属薄膜热力效应的超快热弹性模型。以飞秒脉冲激光辐照金属铜薄膜为例,运用具有人工粘性和自适应步长的有限差分算法,对不同能量密度和脉冲宽度条件下薄膜体内温度场和应力场的变化规律进行了数值模拟,对比分析了电子晶格耦合系数对超快加热过程的影响。结果表明,飞秒脉冲激光辐照早期为明显的非平衡加热过程,电子温度迅速升高,而晶格温度的升高却相对较慢;激光辐照早期的热力耦合效应导致薄膜前表面附近的热应力表现为压应力,随着时间的推移,热应力由压应力转变为张应力,为激光加工和激光对抗提供了理论参考。 相似文献
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黑体辐射法可用于测量电介质内部被超短脉冲激光加工后,电子和晶格的瞬时温度.当一个超短激光脉冲通过物镜聚焦到石英玻璃内部时,在焦点附近诱导出微结构.微结构中热影响区的最大宽度为16μm,热影响区发出的黑体辐射谱通过物镜、带耦合透镜的光纤、光谱仪以及ICCD组装成的系统记录.测试系统收集了电介质内部被单个激光脉冲辐照后,热影响区发射的黑体辐射谱,然后用Planck公式拟合黑体辐射谱,得到电介质温度.电介质被超短激光脉冲辐照后,首先电介质中的价带电子通过强场电离和雪崩电离跃迁到导带,高温高压的等离子体以冲击波的形式向外运动,通过对流方式传递能量,该过程发生在激光辐照石英后21 ns内.21 ns后冲击波转化为声波,中心的气态石英通过热扩散方式影响周围的固态区域,石英温度缓慢下降.在时刻t(单位ns),石英玻璃的温度为5333 exp(-t/1289)K.石英经过3.72μs将冷却到室温,因此重复频率在269 k Hz以上的激光,加工石英玻璃时具有热累积效应. 相似文献
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本文运用分步傅里叶变换,对满足高阶耦合非线性薛定谔方程的超短艾里脉冲与超短高斯脉冲,利用MATLAB数值模拟了在高阶效应下两脉冲相互作用后的演化过程以及时域上的强度变化.获得了负三阶色散效应使超短脉冲相互作用能传输更远距离;正三阶色散效应会减慢超短脉冲相互作用的传输.自陡峭效应通过孤子分裂现象的形式使超短脉冲相互作用产生时域位移.内拉曼效应可以将超短脉冲相互作用的能量由前沿处转移到后沿处. 相似文献
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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。 相似文献
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超快脉冲激光辐照金属薄膜热-力效应的模拟研究 总被引:4,自引:4,他引:0
基于双曲双温两步热传导和热电子崩力模型,考虑到超快脉冲激光辐照金属薄膜材料过程中的热-力耦合效应,得到了完全耦合的、非线性的超快热弹性模型.运用具有人工粘性和自适应步长的有限差分算法,以脉宽为100 fs的脉冲激光辐照200 nm厚金膜为例,对薄膜体内的电子-晶格温度及温度梯度、热应力和电子热流进行了数值模拟研究.结果表明:脉冲辐照早期为明显的非平衡加热阶段,同时形成较大的热电子崩力;电子热流出现双峰现象;超快加热引起的热应力是导致薄膜力学损伤的主要原因. 相似文献
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This paper numerically simulates the process of ablation of an aluminum target by an intense femtosecond laser with a fluence of 40 J/cm 2 based on the two-temperature equation,and obtains the evolution of the free electron temperature and lattice temperature over a large temporal and depth range,for the first time. By investigating the temporal evolution curves of the free electron temperature and lattice temperature at three representative depths of 0,100 nm and 500 nm,it reveals different characteristics and mechanisms of the free electron temperature evolution at different depths. The results show that,in the intense femtosecond laser ablation of aluminum,the material ablation is mainly induced by the thermal conduction of free electrons,instead of the direct absorption of the laser energy; in addition,the thermal conduction of free electrons and the coupling effect between electrons and lattice will induce the temperature of free electrons deep inside the target to experience a process from increase to decrease and finally to increase again. 相似文献
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为了提高脉冲激光制备薄膜的质量,准确掌握电声弛豫时间是关键,它对脉冲激光脉宽和能量密度的选取起着决定性的作用. 文中以铝靶材为例,利用经典的双温方程通过时域有限差分法(FDTD)得到电子、离子亚系统的温度随时间和位置演化的图像,进而得到电声弛豫时间的准确值. 这样便能准确划分热烧蚀和非平衡烧蚀,从而更好地控制激光的烧蚀过程. 同时找出了电声弛豫时间随激光脉宽以及能量密度变化的规律.
关键词:
飞秒激光
电声弛豫时间
双温方程
激光能量密度 相似文献
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S.-S. Wellershoff J. Hohlfeld J. Güdde E. Matthias 《Applied Physics A: Materials Science & Processing》1999,69(7):S99-S107
Femtosecond laser pulses were applied to study the energy deposition depth and transfer to the lattice for Au, Ni, and Mo films of varying thickness. The onset of melting, defined here as damage threshold, was detected by measuring changes in the scattering, reflection and transmission of the incident light. Experiments were done in multi-shot mode and single-shot threshold fluences were extracted by taking incubation into account. Since melting requires a well-defined energy density, we found the threshold depends on the film thickness whenever this is smaller than the range of electronic energy transport. The dependence of the threshold fluence on the pulse length and film thickness can be well described by the two-temperature model, proving that laser damage in metals is a purely thermal process even for femtosecond pulses. The importance of electron-phonon coupling is reflected by the great difference in electron diffusion depths of noble and transition metals. 相似文献
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We theoretically investigated different thermal relaxation participating in the ultrafast thermionic emission processes on gold film surface with a femtosecond pulse excitation. The thermionic emission regimes under the two temperature relaxation and the thermal diffusion relaxation were demonstrated. The simulations showed that the thermionic emission properties can be defined in the regime under two temperature relaxation by reducing the laser fluence, or widening the pulse duration or increasing the laser wavelength. It was also found that there exists a transition between the two distinct thermionic emission regimes under peculiar laser parameters of laser fluence, pulse duration and laser wavelength. The results were explained as significant intervene of laser irradiation parameters into gold film thermal relaxation processes. 相似文献
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Laser short-pulse heating of gold surface is considered and the influence of laser pulse intensity on the temperature and stress fields is investigated. Laser step input pulses with different pulse lengths and the same energy content are employed in the simulations. The electron kinetic theory approach employing thermomechanical coupling is introduced to model the non-equilibrium energy transport in the electron and lattice sub-systems. Thermal stress development in the lattice sub-system and temperature rise in the lattice and electron sub-systems are computed. It is found that electron temperature rises rapidly while lattice site temperature rise is gradual in the early heating period, which is more pronounced for high intensity pulses. Thermal stress component in the axial direction is compressive and its magnitude is considerably less than the yielding limit of the substrate material. 相似文献
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Patrick E. Hopkins 《Applied Surface Science》2007,253(15):6289-6294
Accurate understanding and measurement of the energy transfer mechanisms during thermal nonequilibrium between electrons and the surrounding material systems is critical for a wide array of applications. With device dimensions decreasing to sizes on the order of the thermal penetration depth, the equilibration of the electrons could be effected by boundary effects in addition to electron-phonon coupling. In this study, the rate of electron equilibration in 20 nm thick Au films is measured with the Transient ThermoReflectance (TTR) technique. At very large incident laser fluences which result in very high electron temperatures, the electron-phonon coupling factors determined from TTR measurements deduced using traditional models are almost an order of magnitude greater than predicted from theory. By taking excess electron energy loss via electron-substrate transport into account with a proposed three temperature model, TTR electron-phonon coupling factor measurements are more in line with theory, indicating that in highly nonequilibrium situations, the high temperature electron system looses substantial energy to the substrate in addition to that transferred to the film lattice through coupling. 相似文献