Reactive species created in the collapse of laser-induced cavitation bubbles: Generation mechanism and sensitivity analysis

Reactive species (RS) play a critical role in postoperative complications in the medical application of lasers. From the mechanistic point, the RS arising from laser irradiation are produced from two channels: ionization and dissociation of water in the breakdown plasma, and the violent collapse of the laser-induced cavitation bubble. The latter channel is especially important for nanosecond pulses but poorly understood. In this paper, we conducted a simulation of the chemical reactions coupled with bubble dynamic calculation to quantitatively identify the RS produced in the collapsing bubble. The generation mechanism is explored by the analysis of the reaction pathway. Our calculation shows that while the absolute quantity of the produced RS is small, very high concentrations can be achieved inside the strongly compressed bubble. The initial composition of the bubble recovered from plasma recombination and expansion is found to influence the chemical reactions significantly. Unlike the direct splitting of water molecules in radiolysis and photolysis, the RS productions mainly involve the decomposition of hydrogen peroxide and the reactions between hydrogen, oxygen, and various free radicals. Furthermore, the produced RS is observed to increase with pulse energy as a result of the larger-sized bubbles and more violent collapses. These findings complement our current knowledge of RS in laser surgery and can be used to develop strategies to mitigate the adverse effects or exploit the associated benefits. Published under an exclusive license by AIP Publishing.

Automated summary

Reactive species (RS) play a critical role in postoperative complications in laser surgery. Through simulation calculations, it has been found that the concentration of RS produced in collapsing bubbles is relatively high, and the generation mechanism mainly involves the decomposition of hydrogen peroxide and reactions between hydrogen, oxygen, and various free radicals. Furthermore, the production of RS increases with pulse energy. These findings can contribute to the development of strategies to mitigate complications or exploit the benefits associated with RS in laser surgery.