Optical Manipulation of Water Droplets in Air by a Double-beam Laser Trapping Technique

When micrometer-sized water droplets are levitated in air, thermodynamic metastable states are stable for a long time because they are not affected by the solid surface that provides a scaffold for nucleation. Therefore, it is expected that the use of aerosol droplets as a microreactor would allow chemical processes that are different from those under thermal equilibrium to proceed. The purpose of this study is to construct a double-beam laser trapping system to simultaneously manipulate two water droplets in air, and then to contact and fuse the droplets at an arbitrary timing. Using this system, the effect of surface charge was investigated when water droplets coalesce in air.