The theory of ps and sub-ps laser pulse interaction with metals - II. Spatial temperature distribution

The interaction of short laser pulses with metals is described in terms of a new model involving a generalised nonlocal heat flow in time. The resulting system of coupled differential equations contains additional terms that originate in the thermal inertia of the electron subsystem. They are connected to the time derivative of both the laser intensity and the coupling of the electrons to the phonons. After briefly discussing the importance of the coefficient of heat exchange and of the different contributions to its main parts, the electron-phonon coupling and the average of the squared phonon frequencies, we present snap-shot-like calculations of the spatial temperature distribution along the z-axis for Al, Au, Pb and Nb for different intensities but fixed pulse duration tau(L) = 250 fs. In addition, the electron and phonon temperatures inside a thin Au film are studied in detail. Our results are compared to those arising from a standard two temperature model (TTM) and those of the conventional theory. While the traditional theory becomes invalid in most cases at least in the ps-range the differences between our approach and the TTM become the more pronounced the smaller the coefficient of heat exchange. (C) 1998 Elsevier Science B.V.