Characterizing bubble interaction effects in synchronous-double-pulse laser ablation for enhanced nanoparticle synthesis

To further advance nanomaterial applications and reduce waste production during synthesis, greener and sustainable production methods are necessary. Pulsed laser ablation in liquid (PLAL) is a green technique that enables the synthesis of nanoparticles. This study uses synchronous-double-pulse PLAL to understand bubble interaction effects on the nanoparticle size. By adjusting the lateral separation of the pulses relative to the maximum bubble size, an inter-pulse separation is identified where the nanoparticle size is fourfold. The cavitation bubble pair interaction is recorded using a unique coaxial diffuse shadowgraphy system. This system allows us to record the bubble pair interaction from the top and side, enabling the identification of the bubble's morphology, lifetime, volumetric, and displacement velocity. It is found that the collision and collapse of the bubbles generated at a certain inter-pulse separation results in a larger nanoparticle size. These results mark a significant advancement by controlling the abundance of larger nanoparticles in PLAL, where previous efforts were primarily focused on reducing the average nanoparticle size. The experimentally observed trends are confirmed by numerical simulations with high spatial and temporal resolution. This study serves as a starting point to bridge the gap between upscaled multi-bubble practices and fundamental knowledge concerning the determinants that define the final nanoparticle size.