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

Abstract

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.