Ultra-High-Speed imaging of drop impacts onto liquid surfaces

This talk will present ultra-high-speed video images of novel drop impact phenomena. The video camera used in this work was developed by Etoh \textit{et al.} (2003)\footnote{Etoh, T. G., Poggemann, D., Kreider, G. \textit{et al.} (2003) `An image sensor which captures 100 consecutive frames at 1000000 frames/s'. \textit{IEEE Trans. Electron Devices}, \textbf{50}, No. 1, pp. 144-151.} and will be described in some detail. It can capture 100 images at up to 1,000,000 frames/sec, with 260 by 312 pixel resolution irrespective of the frame-rate used. We study drop impacts onto liquid surfaces revealing ejecta sheets, which form within the first 200 $\mu $s after contact of the drop with the pool liquid. These sheets can self-intersect as well as enclose cylinders of air, to form bubbles on the crown. These sheets are also shown to break up into droplets through the formation of tendrils and a sling-shot. Other experiments show that drops impacting onto very thin layers of liquid, break up in novel ways, through the formation of holes in the ejecta sheets.