Light levitation of microdroplets over a hot liquid-gas interface provides a promising method to manipulate microdroplets. It has been reported that the evolution from a condensed microdroplet to a levitating microdroplet undergoes periodic damped vortex motion. However, the physical mechanism of this phenomenon is still unclear. In this Letter, we clarify the role of laser-induced gas-phase flow, where the laser-driven strong evaporation leads to the gas-phase vortex flow near the heating center. The periodic damped vortex motion of the condensed microdroplet is accordingly attributed to the hydrodynamic interaction between the condensed microdroplet and the laser-induced vortex flow. A damping oscillation model is built to successfully explain the periodic damped vortex motion, and its oscillation average frequency f approximately keeps a scaling law of 1/2 with strain σ and 3/4 with laser power P, i.e., f ∼ σ1/2 ∼ P3/4. This work deepens the understanding of light levitating microdroplet evolution.
Jiang et al. (Sun,) studied this question.