Configurable Vibrational Coupling in Laser-Induced Microsecond Oscillations of Multi-Microbubble System

Microbubbles in liquids dynamically change their volumes through iterative vaporization and gas compression, driving highly localized (≈5 µm) and rapidly oscillating (≈1 MHz) flows. In contrast to an isolated bubble, closely spaced multiple bubbles can potentially induce not only stronger flows but also more complex flow profiles that are spatially and temporally regulated. However, precise on-demand control of bubble distance and the associated interactions between bubbles has remained elusive, limiting their applications in microfluidics. This study demonstrates the induction of two laser-induced microbubbles with configurable separations ranging from 14 to 92 µm with 1 µm precision. These microbubbles self-oscillating at sub-MHz frequencies are generated via photothermal heating, and their dynamics are captured in real-time using a high-speed camera. When the bubbles are in proximity (< 50 µm), their oscillation profiles are in stark contrast to those of an isolated bubble, exhibiting hybridized in-phase and anti-phase vibrations. The distance-dependent evolution of the coupled oscillation frequency, ranging from 0.5 to 0.8 MHz is quantitatively reproduced, using an extended Rayleigh-Plesset equation that accounts for pressure interactions. The findings pave the way for leveraging multiple microbubble arrays to generate complex yet well-regulated spatiotemporal flows previously unattainable in microfluidics.