Fig. 16

Snapshots of jet-droplet ejection from the boiling sample. The video camera speed is 30 fm s ⁻¹, and its exposure time is 1/60 s. a, b & c: run #2 (65 W). The central bright ball is an effect of halation. The actual sample diameter is about one half of the ball. The field of view is ∼35 mm across. In this low laser power (65 W) experiment only the laser spot and its vicinity is above boiling temperature, and hence jet-droplets are ejected in ∼10 o’clock direction where laser beam comes from. a and b are successive video frames. In a, the first jet-droplet is ejected while the jet is still extending for a second droplet. In b, the first and second jet-droplets are seen. The length of their trajectories and the exposure time give their velocities, ∼0.6 m s ⁻¹. d, e & f: run #39-2, #39-1, and #38 (all 100 W), respectively. Thin trajectories tend to elongate longer, indicating that smaller droplets have higher ejection speeds. g, h & i: run #83 (200 W). Experiments with high laser power (200 W) produce jet droplets in all directions because the entire sample are kept above boiling temperature. In g, thick and bent trajectories of several jet-droplets indicate their large size. In h, thin, straight and elongated trajectories stand out, indicating smaller and faster droplets than in g. Rarely a number of droplets are ejected in a fan-like, synchronized fashion, suggesting them being film droplets from a single bubble burst, as shown in i. j: run #32 (200 W). In a late phase of evaporation as shown in j, a thick cloud of condensed, ultra-fine particles, a source of light-scattering, develops and circulates in convective motion