飞秒激光与金纳米薄膜作用中电子弛豫效应的模拟研究
首发时间:2014-09-05
摘要:飞秒激光与金纳米薄膜作用过程中的两步热输送过程常使用抛物线型双温模型来描述。最近,有研究表明,当激光脉宽小于或与电子弛豫时间相当时,抛物线型双温模型不再适用,而应该采用双曲线型双温模型。本文分别使用这两种双温模型与分子动力学相结合的方法,对脉宽为10 fs和100 fs的飞秒激光与金纳米薄膜的作用过程进行了模拟,得到了薄膜电子温度、晶格温度和热应力的分布。结果显示,在不考虑受激电子弹道运动引起的能量输送的情况下,电子弛豫效应对温度和热应力的影响很大;而在计入这一弹道热输送因素时,电子弛豫效应对金薄膜的热应力响应的影响可忽略不计。鉴于实验已明确了金薄膜中能量输送的电子弹道运动效应,可以认为,针对脉宽小于100 fs的超快激光与金薄膜相互作用,可忽略电子弛豫的影响,而且抛物线型双温模型仍然适用。?????
关键词: 计算固体力学 飞秒激光 分子动力学 弹道运动 电子弛豫时间 金薄膜
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A simulation study of the electron relaxation effect in the femtosecond laser interaction with gold nanofilm
Abstract:The two-step heat conduction in the femtosecond laser interaction with gold nanofilm has been largely described by the parabolic two-temperature model. Recently, it was shown that the parabolic two-temperature model is inappropriate for the ultrafast laser-metal interaction when the pulses duration is less than or comparable to the electron relaxation time, and that the hyperbolic two-temperature model should be adopted. In this work, the irradiation of a gold nanofilm by the laser pulses with the durations of 10 and 100 fs is simulated by the methods combining the parabolic and hyperbolic two-temperature models with the framework of molecular dynamics. The distributions of the electron and lattice temperatures and stresses in the nanofilm are obtained. Numerical results show that the effect of electron relaxation on the material responses is significant when the energy transport due to the ballistic motion of excited electrons is not considered. Instead, this effect is found trivial with including the ballistic heat transport. Since the energy transport by the electron ballistic motion has been experimentally confirmed for gold, it is concluded that for the sub-100-fs laser interaction with gold the electron relaxation effect could be neglected and the parabolic two-temperature model is still valid.
Keywords: Computational solid mechanics Femtosecond laser Molecular dynamics Ballistic motion Electron relaxation time Gold thin film
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