超快激光脉冲作用下金薄膜温度和介电函数变化的研究

Change of temperature and dielectric function for Au thin film under ultrafast laser radiation

金薄膜在表面等离子体共振和表面增强拉曼散射等方面有着广泛的应用,其介电函数受到温度和入射光波长的影响较大。超快激光脉冲具有脉冲宽度短和能量密度高的特点,用其作为一种热源成为研究薄膜材料热传导过程的一个有效手段。从金薄膜的介电函数随波长变化规律出发,结合Lorentz-Drude模型,得到可见光和近红外区域不同温度下金纳米薄膜的介电函数的实部和虚部变化,推导得到不同温度下金纳米薄膜反射率的瞬时变化。使用双温模型得到温度随时间的变化,进一步可以直接带入得到激光脉冲作用下的反射率随时间的变化关系,与实验测量结果比较可加深对激光脉冲加热金属薄膜方面研究工作的理解。

Au thin film has applied extensively in the field of Surface Plasmon Resonance （SPR） and Surface- enhanced Raman Scattering （SERS）. Ultrafast laser pulse has the characteristics of short pulse width and high energy density as a kind of heat source, and it has become an effective method to study the thermal conduction process of thin film materials. From the dielectric function of the Au thin film with the wavelength change, we can get the change of real and imaginary part of Au thin film dielectric function in visible and near infrared region under different temperature can be derived. Using the two-temperature model, temperature change with delay time is obtained, and the transient reflectivity under laser pulse radiation is derived directly. Theoretical simulation on heating metal film with laser pulse can help us to deepen the understanding of the experimental results.