Laser-induced vapor bubbles in subcooled water: From nucleation to collapse and jet formation

The collective dynamics of an ensemble of vapor bubbles during laser-induced boiling of a subcooled liquid was studied using high-speed visualization. The re-formation of vapor bubbles was initiated by prolonged exposure to continuous laser radiation transmitted through an optical fiber. This boiling is characterized not only by the nucleation, growth, and subsequent collapse of numerous bubbles but also by the formation of high-speed submerged jets. We found that the most powerful and fastest jets, penetrating farthest from the end of the fiber, are initiated by the collapse of bubbles, the radius of which is several times the radius of the fiber. The frequency of formation of these large bubbles strongly depends on the laser power. The results of the analysis showed that the formation of the conditions necessary for the appearance of bubbles is a highly nonlinear process, in which previously formed vapor bubbles play important role by directly impacting the thermal and hydrodynamic conditions. Thus, models based only on the dynamics of individual bubbles are insufficient to fully describe the boiling process under prolonged exposure to a laser. The results obtained are important for the development and optimization of applications such as minimally invasive laser surgery and precision microprocessor processing.