Laser irradiation of differently aged carbon nanoparticles: effect on optical properties

The effect of laser irradiation on carbon nanoparticles of different maturity sampled from a premixed flame is investigated. To this purpose, extinction and laser-induced incandescence measurements are carried out on pristine and pre-irradiated nanoparticles. From extinction measurements, a spectral trend of the absorption coefficient of the particles is retrieved. Moreover, two-color laser-induced incandescence versus fluence is used to investigate the behavior of signal and temperature fluence curves in the different conditions under analysis. By coupling these results, interesting outcomes are obtained depending on the nature (nascent vs mature) of the particles. For nascent particles, a significant shift of the fluence curves is observed for the pre-irradiated particles, suggesting an increase in the absorption efficiency. However, no changes in the spectral trend of the absorption coefficient are observed from extinction measurements. On the contrary, for mature particles the absorption properties are strongly affected by irradiation resulting in an increase in the absorption efficiency in the spectral region below 600 nm. Moreover, a decrease of the saturation temperature for pre-irradiated mature particles towards the temperature value reached by nascent particles is observed. Two processes, namely fragmentation and sublimation followed by nucleation of new particles are suggested to occur under laser irradiation, especially for mature soot particles.