Nonlinear characteristics of laser-induced incandescence of rough carbon surfaces

Abstract

In this work the possibility of laser overheating of light-absorbing surfaces of bulk carbon samples to incandescent temperatures with the use of a moderate-power Q-switched YAG-Nd 3+ laser (wavelength 1064 nm, pulse duration 20 ns, power density 3-10 MW/cm 2 ) was studied. We observed laser-induced incandescence (LII) of carbon surfaces and investigated its properties. When the surface was irradiated by a sequence of laser pulses, unusual changes of LII intensity were discovered in the experiments. Also significant nonlinearity in the dependence of LII intensity on the laser pulse power density was observed. The average temperature of irradiated surface was estimated by approximating the experimental LII spectrum by Plank's function and by computer simulations of laser heating of the carbon surface. For typical experimental conditions, the value of 2400 K was obtained. Both of the estimates of temperature are in a good agreement. The model, which is proposed to explain the observed effects, is based on the equation of heat conduction. Well-known thermal and optical properties of carbon are taken into account. The observed effects can be explained by essential nonuniformity of heating of rough surfaces and dominant evaporation of carbon from the tops of surface asperities.