Optimizing laser ablation in liquid: The role of ablation region confinement

In the present work, pulsed laser ablation in liquid (PLAL) experiments have been conducted on a disk-shaped copper (Cu) target with a confined ablation region. Nanoparticles (NPs) are synthesized by employing a flat target and targets with valley (channel) widths of 4 and 3 mm to investigate the effect of confinement on properties of NPs. On the flat target, Cu NPs exhibiting bimodal size distribution with average sizes of 8 and 23 nm have been produced. In contrast, monomodal NPs are synthesized in confined valleys, with average sizes decreasing to 4 and 6 nm for 4 and 3 mm valleys, respectively. To understand the influence of confinement on cavitation bubble dynamics, shadowgraphy investigation is employed. The study revealed that the bubble size increases as the valley width decreases. The Gilmore model has been used to estimate the temperature and pressure within the bubble, indicating that both the parameters enhance with confinement. The shadowgraphy results suggest that the reheating of the ablation region due to shockwave interaction with the valley walls is the primary factor influencing the NP properties and cavitation bubble dynamics.