Abstract

Electron heating in metals by ultrashort laser pulses has been under intensive investigations in recent years^1,2. It is generally believed that in a very short time (< 1-2 fsec) after the optical excitation, the electrons equilibrate among themselves via the electron-electron interaction, and establish a thermal Fermi-Dirac distribution at an elevated temperature. The electron-phonon interaction operates on a longer timescale of several psec to equilibrate the electrons with the lattice phonons.^1,2 During those several psec, the electrons are decoupled from lattice and it is possible to heat the electrons alone up to several thousand K. However no direct measurements of the electron energy distribution function in laser-heated metals have been reported so far. We have used ultraviolet photoemission spectroscopy to directly obtain the energy distribution function with 500 fsec time resolution. We confirm that on this time scale, the distribution is well described by a Fermi-Dirac function and we thus directly measure the time-dependence of the electron temperature.

© 1991 Optical Society of America