Anisotropy of Laser-Induced Thermal Emission of Rough Carbon Surfaces

In this paper, the visible thermal emission of carbon materials under the irradiation by nanosecond infrared laser pulses is investigated. For rough carbon surfaces, the experiments show that the pulse length of laser-induced thermal emission depends on the direction of observation. In particular, in the case of observation along the material’s surface, the duration of the emission pulse is typically 20÷40% longer than in the direction perpendicular to the surface. For the explanation of the observed anisotropy of the kinetics of laser-induced thermal emission, a calculation model is proposed, which accounts for significant heterogeneity of pulsed laser heating of rough surfaces. The computer modeling predicts that peaks and valleys of the surface relief can be heated to significantly different local temperatures, and the temperature relaxation in the relatively hot peaks is longer than in the relatively cold valleys. As a result, when the laser-induced thermal emission is observed along the surface, the valleys are shadowed by the peaks, and this circumstance leads to the observed anisotropy of thermal emission kinetics. The results of the computer simulations with regard for the effect of shadowing are consistent with the results of measurements.