Evaporation of solids by laser pulses. I. Iron

Abstract

The laser−induced vaporization of iron was studied using a quadrupole mass spectrometer detector. Neutral atoms emitted by thermal processes at the surface were of interest; energetic ions produced by a plasma near the surface were not. Conventional mode laser pulses served as a heat source and the characteristics of the pulses of vaporized atoms reaching the mass spectrometer were determined by time−of−flight analysis of the output signal from this device. The data agreed reasonably well with the predictions of an equilibrium model, in which transient surface vaporization is treated as a sequence of equilibrium stages at each of which Langmuir vaporization with unit condensation coefficient occurs. Agreement between theory and experiment failed at high laser energies because of the outward flow of molten iron from the spot struck by the laser. This cratering phenomenon invalidated the temperature calculation from which the vaporization rate was calculated.