The Theory of Laser Materials Processing

Abstract

In this chapter some aspects of the interaction of femtosecond laser pulses with metals has been considered and compared with the effects of longer pulses. The most important point is, perhaps, that metals exposed to femtosecond laser pulses are no longer in local thermal equilibrium. On short time scales the electron and phonon subsystem are decoupled and may have very different temperatures. Moreover, the electrons are governed by a nonequilibrium distribution and not by the Fermi-Dirac distribution even for low intensities. In many cases, depending on the value of the electron temperature relaxation time, the parabolic heat conduc-tion (TTM) is no longer suitable for the determination of the electron temperature distribution and should be replaced by the ETTM.