3.1.2. Driving at 200 kHz
Here the cuvette setup is used again but now imaged in top view with the Brandaris 128 high-speed camera. The driving frequency is approximately twice the linear resonance frequency (98 kHz) of the pit and lies below the first higher harmonic of 243 kHz . Similar to previous observations, there is a threshold for the pressure above which bubble pinch-off occurs corresponding to an input power of 50 mW. Interestingly, in the regime below this RJR-2403 threshold the liquid–gas interface exhibits alternating dark and bright rings which appear to move radially outward periodically with the driving frequency (see Fig. 6(a)).
Fig. 6. Four sequences of frames taken from high-speed recordings in reflective imaging mode (top-view) of the pit for increasing driving input power. Sequence (a) is ascus at approximately 45 mW showing ring-structures. Increasing the driving power to 50 mW induces interface deformation and pinch-off (b). Further increase (79 mW in (c) and 235 mW in (d)) both increases the bubble number and maximum expansion. Note the different scale in (d). Supplementary Video.Figure optionsDownload full-size imageDownload as PowerPoint slide