Femtosecond thermoreflectivity and thermotransmissivity of polycrystalline and single-crystalline gold films

Abstract

A femtosecond laser is used to generate and probe hot electrons in polycrystalline and single-crystalline thin gold films. Transient thermoreflectivity and thermotransmissivity measurements are performed. The hot-electron energy-loss lifetime is shown to be 1–3 ps and increases with laser fluence. For film thicknesses comparable to the optical skin depth, the lifetime for polycrystalline films is slightly shorter than that for single-crystalline films. For thicker films, hot-electron transport competes with energy loss. Electron transport appears to be slower in the polycrystalline films.