Observation of laser-induced ablation in silicone oil under varying focal conditions

We investigate the effect of focal position on laser ablation of a solid target in silicone oil using photoelasticity imaging technique. By varying the focal plane relative to the target surface, we observe distinct changes in plasma formation, shockwave behavior, and stress wave strength. Results show that the strongest mechanical effect occurs slightly above the focus, where plasma confinement enhances energy density and stress delivery. In contrast, at-focus and under-focus positions lead to weaker stress due to breakdown in the liquid. These findings offer valuable insight for optimizing under liquid-laser-ablation-based applications requiring precise mechanical control, such as laser peening, micromachining, and nanoparticle synthesis.