Identifying the influence of bubble size and position on crater formation during underwater nanosecond laser ablation of stainless steel

Abstract

AbstractUnderwater laser ablation can be employed both as a means to produce nanoparticles and to texturize surfaces of various materials. In this approach, a stationary or flowing water layer above the target surface confines laser induced plasma which cools to form short lived cavitation bubbles, positively influencing the amount of removed material per laser pulse. Plasma and cavitation bubble evolution additionally give rise to bubbles which may persist in the water throughout the ablation process. These bubbles are known to have a detrimental effect on material removal rates particularly in stationary water, but the quantitative influence of bubble dimensions and position on removed material volume is currently unknown. Here we show the laser intensity profile changes induced by bubbles located at 0–0.4 Rayleigh lengths above a stainless steel surface and couple these changes to removed crater volume. Our results show that water flowing at Reynolds numbers in the range of 1–100 positively contribute to crater volumes for pulse frequencies up to 1 kHz. At 1 kHz, it was found bubbles have insufficient time to flow from the vicinity of the laser spot, regardless of the Reynolds number within the range investigated. These conclusions assist in selecting an appropriate combination of laser and flow conditions to optimize laser ablation material removal rate.