ALUMINUM 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 durat ion, 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 disp layed, which confirms earlier observations with gold and tungsten. Thi s nonlinearity is consecutive to the non-thermal distribution of elect ron gas of laser-heated metal on the time scale of the electron-phonon relaxation time. Analysis of experimental data, using the model previ ously developed by us [1], gives a value of electron-phonon relaxation time approximate to 0.55 +/- O.11 ps.