Nonthermal radiation from a metal surface excited by a laser

An investigation was made of the radiation emitted from a metal surface excited by laser pulses of moderate intensity (less than 2 × 10⁸ W/cm²). It was found that in the field of the parameters q and τ_p (where q is the intensity and τ_p is the duration of the laser pulse) there are two regions in which physically different mechanisms lead to the emission of radiation from the surface. The characteristics of the surface radiation emitted by a single crystal of tungsten illuminated by long (250 μsec) and short (60 nsec) ruby laser pulses were experimentally investigated. It was found that in the first case the radiation was produced by heating of the surface, while in the second it was of a nonequilibrium nature and resulted from deformation of the distribution function of the electrons in the metal in the laser radiation field. An expression was obtained describing the spectral intensity of the nonequilibrium radiation in the visible region.