The anomalous thermal radiation of metals produced by ultrashort laser pulses

Abstract

The spectral-time characteristics of the secondary radiation produced in silver and tungsten by picosecond laser pules of varying duration and fluence (energy density) have been studied theoretically and experimentally. It is established that the secondary radiation is due to heating. In silver, however, it is not usual and does not correspond, for example, to grey body radiation. This radiation — the anomalous thermal radiation — is defined by the following mechanism. When the electron and phonon subsystems in a metal are heated (including also the nonisothermal process), there appears the glow with the continuous spectral distribution and the intensity exceeding the radiation intensity of the grey body whose temperature is equal to the temperature of the ion or electron subsystem of a metal. This anomaly is either due to overheat of the electron subsystem with respect to the ion subsystem or due to recombination of electrons and therm-ions in a microlayer above the metal surface.