Aluminium electron-phonon relaxation-time measurement from subpicosecond nonlinear single-photon photoelectric emission at 248 nm

The sensitivity of photoelectric emission of polycrystalline aluminium, produced by 248 nm laser pulses with p-polarization and 450 fs duration, under incidence angles theta = 74-86 degrees, has been measured. A nonlinear increase of photoemission efficiency, as a function of the incident laser peak intensity in the range of 1-50 GW/cm(2), was displayed, which confirms earlier observations with gold and tungsten. This nonlinearity is consecutive to the non-thermal distribution of electron gas of laser-heated metal on the time scale of the electron-phonon relaxation time. Analysis of experimental data, using the model previously developed by us [1], gives a value of electron-phonon relaxation time approximate to 0.55 +/- O.11 ps.