Origin of High Ablation Efficiency of Sub-nanosecond Laser Ablation in Liquid Revealed by Pump-probe Microscopy
* Presenting author
Abstract:
Laser ablation in liquid provides a versatile and safe nanoparticle production method. However, due to laser-liquid and laser-target interactions a significant amount of energy dissipates and is no longer available for the ablation process. The energy dissipation mechanisms include: linear and non-linear absorption by the liquid, attenuated stress confinement, re-deposition of and shielding by ablation products and finally shielding and scattering at the emerging cavitation bubble.It has been shown that attenuated stress confinement as well as re-deposition and shielding processes in air occur on a time scale ranging from about 5 ps to about 1 ns. During this temporal range the ablation efficiency is significantly reduced. After approximately 1 ns the ablation efficiency is recovering in air.By using pump-probe microscopy, we reveal that shielding mechanisms in air and water are comparable up to approximately 2 ns after pulse impact. When 2 ns are exceeded, the ablation dynamics in liquids start to differ from the ablation dynamics in air. This characteristic time is identified as the onset of cavitation bubble formation. Accordingly, pulse durations in the range of several hundred ps to 2 ns facilitate highly efficient NP production due to reduced ablation product and cavitation bubble shielding.