Gram Scale Synthesis of Pure Ceramic Nanoparticles by Laser Ablation in Liquid

Scale-up criteria of laser ablation in the liquid phase with nanosecond pulses is studied for efficient generation of pure ceramic nanoparticles in an aqueous environment. Besides high laser fluence and low height of the applied liquid layer, specific pulse overlap and defined laser repetition rate are required for significant enhancement in nanoparticle productivity. The ablation rate increases by 350% by reducing the liquid film from 8 mm to 2.5 mm owing to reduced absorption and scattering of the incident laser beam by previously ablated nanoparticles. The controlled interpulse distance yields a further increase in material removal rate by another 300% compared to machining in the pulse overlap mode. The residual cavitation bubble from the previous laser pulse and the dispersed nanoparticle interaction with the following laser pulse and optimized temperature gradient in the lattice of the target are assumed to alter productivity. This hypothesis is confirmed by varying the repetition rate with equal laser fluence and pulse overlap, which causes a drastic rise in nanoparticle productivity by a factor of 65. A maximum corundum nanoparticle productivity of 1.3 g/h with Feret particle size of 30 nm is gained by 18.5 W of focused laser power at 4 kHz of repetition rate, providing 125 μm interpulse distance and liquid flow.