Investigation of nanoparticle formation during surface decontamination and characterization by pulsed laser

The production of ultrafine and nanoparticles from a surface is dependent on the laser energy and laser wavelength used to treat and on the material used to construct the surface. Under dry conditions, the minimal laser fluence (mJ cm^-2) required to produce a detectable amount of particles was found to be the greatest for a pure material, alumina, then for a complex mixture, concrete, with the least for a simple mixture, stainless steel, using both visible (532-nm) and UV (266-nm) laser wavelengths. The threshold energy requirement was found to be significantly higher when a shorter laser wavelength was used. The results indicate that for a given amount of laser energy used, there are more than twice the particles produced when a 532-nm wavelength is used than a 266-nm, although a 266-nm photon has 2 times more energy than a 532-nm. For both wavelengths, the total number concentration of produced particles is found to be linearly proportional to laser fluence. The correlation of the log-log linearity is excellent, indicated by a R² value close to 1 for all materials. The models were derived, empirically, for predicting the amount of particles that could be removed from the surface of different materials using different lasers operated at low fluence conditions.