FEMTOSECOND THERMOREFLECTIVITY AND THERMOTRANSMISSIVITY OF POLYCRYSTALLINE AND SINGLE-CRYSTALLINE GOLD-FILMS

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.