Picosecond and Femtosecond Laser Machining May Cause Health Risks Related to Nanoparticle Emission

It is well known that nanoparticles are generated as by-products during ultrashort-pulsed laser ablation. Airborne nanoparticulate matter is well known as potential health risk when workers are exposed during operation of laser machinery. In order to provide safety-related statements on nanoparticles generated during laser micromachining, we studied the particle size distribution during picosecond (ps) and femtosecond (fs) laser ablation. 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 7 nm sized particles during machining of metals (steel, brass) and ceramics (zirconia). These nanoparticles sampled at the workplace have the same chemical composition than the ablated material (iron-chromium-nickel alloy, yttria-doped zirconia). A quantitative risk assessment is carried and compared with indicators of toxicological effects of inhaled nanoparticles. The surface equivalent of the nanoparticles dispersed in the air of the workplace is not likely to exceed the surface dose which cause inflammatory response in animal lung. But within one 8 h shift, the background level is exceeded by a factor of 20 so that efficient fume extraction is strongly recommended for safe operation during fs and pf laser micromachining even in research laboratories.