Abstract. Laser-induced incandescence (LII) of silicon surface is investigated under the excitation by a Q-switched YAG:Nd laser. With the increase of laser irradiation dose, the increase of LII signal is observed, which is attended by visible changes of the surface geometry. The anomalous behavior of the parameter of non-linearity of LII is observed with the increase of laser excitation power.Keywords: laser-induced incandescence, silicon, laser surface processing.Manuscript received 27.08.12; revised version received 25.09.12; accepted for publication 17.10.12; published online 12.12.12.

The relaxation kinetics of laser-induced scattering and absorption was investigated in a liquid epoxy resin suspension of carbon microparticles. The scattered light intensity and the optical transmittance at temperatures below +10 o C demonstrate anomalous kinetics with a distinct build-up stage. The observed behavior is interpreted as a manifestation of processes of mechanical stress relaxation in epoxy layers around microbubbles. The microbubbles induced by laser irradiation of the suspension can be a tool for the investigation of mechanical stress relaxation in polymers. Keywords: suspension of carbon microparticles, induced scattering and absorption, mechanical stress relaxation in polymers.Introduction. Light-absorbing microparticles interact with powerful pulsed laser radiation (LR) to produce several effects of scientific and applied interest. Thus, pulsed LR heats the particles in aqueous suspensions of carbon microparticles about 0.1 μm in size to temperatures of the order of several thousands of degrees. This forms microbubbles filled with products from vaporization and interaction of water with the red-hot carbon [1-3]. The microbubbles induced by the LR increase light scattering in the irradiated region of the suspension. The bubbles increase to sizes of 0.1 μm during the action of the laser pulse (~10 -8 s). As a result, a decrease of the optical transmission of the suspension is observed both during the action of the laser pulse and after it is finished (optical limitation effect). Optical limitation in aqueous carbon suspensions is characterized by a considerable change in the shape of the passing laser pulse [3]. Emission in the attenuated region of the passing laser pulse is weakened because of light scattering on the microbubbles formed during the action of the laser pulse front.Optical limitation in carbon suspensions is accompanied by incandescence of microparticles heated by the laser [3][4][5][6][7][8]. Their luminescence is clearly visible to the unaided eye during IR laser excitation. Laser-induced incandescence (LII) of carbon microparticles was first discovered and studied in detail in flames and internal combustion engine exhaust gases where microscopic soot particles are formed during combustion of fossil fuel [9].LII and optical limitation were observed not only in aqueous suspensions but also in other transparent matrices doped with carbon microparticles such as toluene [10], polymeric matrices [11], and oxide glasses [12]. However, such anhydrous carbon suspensions were studied in less detail than the aqueous suspensions.Rapid heating by LR of carbon microparticles in polymeric matrices causes pyrolysis and thermal decomposition of the polymer around the hot particles. Pyrolysis produces significant changes in the structure and properties of the absorption and scattering centers. As a result, polymeric carbon suspensions exhibit persistent changes of the optical transmission as a result of LR irradiation [11].The size of microparticles irradiated by LR decreases in aqueous carbon su...

Laser-induced incandescence (LII) of rough carbon surfaces was studied under the Q-switched YAG:Nd laser excitation. For the surfaces irradiated by a sequence of laser pulses, the nonmonotonic behavior of LII intensity with the increase of number of irradiating laser pulses was observed. Computer simulation of pulsed laser heating of rough carbon surfaces revealed essential non-uniformity of the temperature field on the irradiated surface hence the surface relief is affected by the laser irradiation due to the processes of evaporation of the peaks on the irradiated surface. The intensity of LII was calculated as a function of height of the surface roughness. The results of calculations explain the observed features of LII of carbon surfaces.

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