基于飞秒瞬态反射/透射技术的纳米Au半透膜热效应研究

以飞秒激光放大器作为光源联合使用瞬态反射/透射实验技术研究了纳米Au半透明纳米薄膜中非平衡载能粒子的热传导过程. 在相同实验条件下, 发现该薄膜的瞬态透射和反射信号明显不同并且延迟时间在5.0–7.5 ps时瞬态透射信号的符号发生改变. 对纳米薄膜的透射和反射信号进行了对比分析, 分别使用双温模型和Crude近似进行数据模拟并拟合, 分析认为沿膜厚方向的温度梯度变化和界面热阻效应引起介电函数的变化不同, 从而引起了瞬态透射信号和反射信号的不同. 对于半透明金属纳米薄膜需要同时考虑其瞬态透射和反射影响才能得到准确的瞬态吸收结果. 随着抽运脉冲能量的增加, 可以看到上升时间约为1.0 ps, 电子-晶格弛豫时间增加.

Thermal effect of translucent gold nanofilm based on transient reflection/transmission technique

In this work, the relaxation dynamics of optically excited electrons and lattice in translucent gold nanofilms is measured with femtosecond transient reflection and transmission technique. In order to investigate the mechanisms of heat transfer in metal nanofilm theoretically, the two-temperature model and the Crude-model approximation are used to estimate the profile of decays and the temperature of electrons and lattice. Ultrafast relaxation dynamics of gold nanofilm 60 nm in thickness is different obviously in transient reflection and transmission measurements. Electron-lattice coupling effect in the transmission method is stronger and more sensitive than that in the reflection method under the same experimental conditions. Gradient change of temperature along the direction of film thickness and interface thermal resistance due to the boundary scattering should be responsible for the difference between them. Experimental data suggest that both transient reflection and transient transmission of translucent films should be considered together in the investigation on the mechanism of heat transfer. With increasing energy of pump laser pulse, the rise time is about 1.0 ps, and the electron-lattice relaxation time becomes longer.