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金属材料中的热波现象可以利用包含电子弛豫时间影响的双曲两步模型进行理论分析.通过飞秒激光热反射实验系统对金属薄膜材料进行了测量.利用偏振分光棱镜将飞秒激光分成抽运光和探测光,其中较强的抽运光用于加热金属薄膜而较弱的探测光用于探测薄膜表面反射率随时间的变化,两束光之间的光程差通过步进电机进行精确控制.利用金属薄膜反射率和电子温度的正比例关系就可以得到电子温度随时间的变化规律.实验发现在加热激光脉冲过后的电子温度下降区间会出现另一个较弱的电子温度波峰,并利用相同厚度的两块金属薄膜样品重复测量对实验结果进行了验证.理论上这一现象可以解释为金属薄膜中热波在背面反射的结果,并且实验结果和双曲两步模型给出的热波理论计算结果相符合.根据实验结果计算出热波传递速度约为5×105m/s,对应的电子弛豫时间为60fs.
The thermal wave phenomenon in metallic materials can be theoretically analyzed by the hyperbolic two-step model including the influence of electron relaxation time.Metal film material was measured by the femtosecond laser thermal reflection experimental system.The femtosecond laser was split into Pumping light and probe light, of which strong pump light is used to heat the metal film and weak probe light is used to detect the film surface reflectance with time, the optical path difference between the two beams through the stepper motor And the precise control of the electron temperature can be obtained by using the proportional relationship between the reflectance of the metal film and the electron temperature.The experiment shows that there is another weaker electron temperature peak after the laser pulse is pulsed, The experimental results were validated by repeated measurement of two metal thin film samples with the same thickness.Theoretically this phenomenon can be interpreted as the result of the reflection of the heat wave in the metal thin film on the back surface and the experimental results and the heat given by the hyperbolic two-step model Wave theory calculation results are consistent.According to the experimental results calculated heat wave velocity of about 5 × 105m / s, the corresponding electronic relaxation Time is 60fs.