铜膜中激光诱导超声波传播特性的理论和实验研究

发布时间：2018-04-05 02:09

  本文选题：激光超声　切入点：数值模拟　出处：《哈尔滨工业大学》2016年硕士论文

【摘要】：飞秒激光与物质相互作用的机理性的研究对认识物质各项弹性参数对激发出的超声波的影响有着非常重要的意义。人们还可以根据对超声表面波的检测表征材料表面的缺陷。在许多理论机制的研究中,学者们首先考虑激光使得材料表面具有一定的温度场,然后温度场产生热应力,最后热应力又引起形变。在温度场模型的选择上许多学者还是倾向于抛物线型的热传导方程,但是对于超短脉冲激光,双温模型才能比较好的描述温度场。针对超短脉冲激光与金属膜相互作用时间短的特点,基于电子及晶格的双温模型,构建了激光加热金属膜的热沉积模型,并给出了热场的时间演化数值解,得到了电子和晶格热平衡的时间。基于热弹效应,构建了应力场的时空演化方程,并给出了应力场的时空演化数值解,得到了激光驱动应力波在金属铜膜中的传播速度。基于应力与形变的转换关系,数值模拟了飞秒激光作用下铜膜中位移场的分布情况,分析了超声纵波在铜膜中的产生和传播情况。在实验部分本文设计并且搭建了泵浦探测超快摄影平台,利用应力波在材料中传播时会产生双折射效应,在铜膜样品前后加了一组消光的偏振片作为超快快门,以图像的形式研究了飞秒激光在铜膜表层激发出的超声波的传播过程,给出超声波在铜膜表层中传播的速度。
[Abstract]:The study of the mechanism of femtosecond laser interaction with matter is of great significance in understanding the effect of various elastic parameters of matter on the excited ultrasonic wave.The defects on the surface of the material can also be characterized by ultrasonic surface wave detection.In the study of many theoretical mechanisms, the researchers first consider that the laser makes the surface of the material have a certain temperature field, then the temperature field produces thermal stress, and finally the thermal stress causes deformation.In the choice of temperature field model, many scholars still prefer parabola heat conduction equation, but for ultrashort pulse laser, the double temperature model can describe the temperature field better.In view of the short interaction time between ultrashort pulse laser and metal film, the thermal deposition model of metal film heated by laser is constructed based on the double temperature model of electron and lattice, and the numerical solution of time evolution of thermal field is given.The time of thermal equilibrium of electron and lattice is obtained.Based on the thermoelastic effect, the space-time evolution equation of the stress field is established, and the numerical solution of the space-time evolution of the stress field is given, and the propagation velocity of the laser-driven stress wave in the copper film is obtained.Based on the relationship between stress and deformation, the distribution of displacement field in copper film subjected to femtosecond laser is numerically simulated, and the generation and propagation of ultrasonic longitudinal wave in copper film are analyzed.In the experiment part, we designed and built the pump detection ultra-fast photography platform. Using the stress wave propagating in the material will produce birefringence effect, adding a group of extinction polarizers before and after the copper film sample as the ultrafast shutter.The propagation process of ultrasonic wave excited by femtosecond laser on the surface of copper film is studied in the form of image, and the velocity of ultrasonic wave propagating in the surface layer of copper film is given.
【学位授予单位】：哈尔滨工业大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：TN249;O426.2
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本文编号：1712713