Ultrafast relaxation of electrons probed by surface plasmons at a thin silver film

We present a novel subpicosecond optical transient-reflection method, which employs the surface-plasmon resonance of a thin silver film as a very sensitive probe to study small transients of the effective electron and lattice temperature. By measuring under surface-plasmon resonant and nonresonant conditions, we can discriminate between lattice and electron heating. We find a change of the lattice and electron temperature of respectively, Δ$T_l$=0.10(5) K and Δ$T_e$=30–90 K for an intensity of 180 W ${\mathrm{cm}}^{\mathrm{-}2}$ and an electron-phonon energy relaxation time of 670(70) fs.