Health risks of nanoparticulate emissions during femtosecond and picosecond pulsed laser machining

摘要

Nanoparticles are known to cause adverse health effects. But the generation of nanoparticles cannot be avoided during laser machining, especially ultrashort-pulsed laser ablation which releases a high share of nanoparticles. The nanoparticulate size fractions emitted during picosecond (ps) laser ablation are compared with those released during femtosecond (fs) laser ablation using steel, zirconia and brass. At the same pulse energy, fs pulses release similar share of nanoparticles (>80%) in the aerosol fraction, with fs compared to ps generating a far higher share of ultrasmall (7 nm) sized particles during machining of metals and ceramics. The frequency maximum corresponds to the particle size of 50 nm independently of the ablated material and applied pulse duration. During ps laser ablation the absolute nanoparticle emission rate is higher than during fs laser ablation, whereas the emission rate per pulse is two magnitudes lower. Finally, the nanoparticle emission rates and its nanoparticle surface equivalent for ps and fs laser micromachining of metal and ceramic are compared with inflammatory thresholds derived from toxicology studies. It would take more than 6.500 working days to exceed this theoretical threshold of inflammation during laser operation at 0.5-2W and at least 260 working days using high-power lasers.