Sub-nanosecond pump-probe analysis of metal targets during nanoparticle generation by laser ablation in liquid and air

The goal of this proposed project is to extend the current field of knowledge in the area of nanoparticle synthesis generated through pulsed laser ablation in liquids (LAL). This will be achieved through advanced time resolved experimental techniques and nanoparticle characterisation methods. The field of nanoparticle synthesis has seen widespread growth due to increasing supply demands in a wide range of application across diverse fields such as life and material sciences. Recently the use of ultrashort laser sources has gained traction as a viable method for the production of colloid nanoparticle solutions, with recent reports demonstrating high yields in the region of grams per hour. While recent trends in nanoparticle productivity have demonstrated promising growth, further increases are necessary in order to push LAL as a commercially viable method for nanoparticle synthesis. The current increase in nanoparticle productivity has been accelerated through advances in laser and optical technology. However, in terms of a fundamental understanding of the interaction between ultrashort laser pulses and the target material, the current understanding has been primarily through theoretical studies consisting of molecular and hydrodynamic models. These studies indicate that the initial nanoseconds after the pulse impact play a crucial role in the development and production of nanoparticles in a liquid environment. Current experimental techniques in this field have failed to investigate these early time intervals, and as such there are many open questions as regards to nanoparticle formation. This project proposes to open up this field of study through the combination of both advanced picosecond resolution pump-probe experiments at MUAS and through state of the art characterisation techniques at UDE. At MUAS the experiments will focus on time-resolved pump-probe ellipsometry and microscopy of metal targets in an air and liquid ambient, which will probe with high time accuracy the evolving dynamics (both quantitatively and visually) of the ablation process, and give a unique insight into the formation of nanoparticles in the critical early time stages. At UDE, advanced characterisation of the nanoparticles will reveal a complete picture of the dependence between nanoparticle formation and applied parameters such as laser power, pulse duration and number of incident pulses. Taking these areas into consideration will allow a highly advanced insight into the nanoparticle processes, including nanoparticle formation on a picosecond-nanosecond time scale, dependence of nanoparticle formation on pulse duration and the effect of pulse incubation on nanoparticle formation. This study of the nanoparticle formation mechanisms and dynamics can be used to drive and inform methods to increase nanoparticle productivity, as well as providing valuable fundamental insights into the interaction of laser pulses with metals.