Mechanism of cavitation-acoustic emission in biomimetic plant vessels with fiber-tip Fabry-Pérot microcavities

The acoustic emission phenomenon observed in plants with xylem structures under drought or mechanical stress has attracted significant research interest due to its underlying physical mechanisms. The most widely accepted hypothesis attributes this phenomenon to vibration caused by cavitation-induced microbubbles within xylem conduits. However, direct experimental evidence supporting this mechanism remains elusive. In this work, we propose a biomimetic approach to investigate cavitation-driven sound generation by replicating plant vessel cavitation using fiber-tip Fabry-Pérot (F-P) microcavities. A femtosecond laser two-photon 3D lithography technique was employed to fabricate annular microchannel structures mimicking plant vessels on optical fiber tips. When immersed in liquid, the gas-liquid interface and fiber end-face collectively form an F-P cavity. Vibrations of the gas-liquid interface induce detectable shifts in cavity length, manifested as resonance peak modulations. Two mechanisms causing gas-liquid interface vibration were observed in the experiment: stick-slip jumping during interface propagation within microchannels, coalescence-induced oscillations between condensate droplets and the interface. Both mechanisms generated interface vibrations within the 20-100 kHz frequency range, consistent with acoustic emissions reported in plant studies. This work provides indirect but compelling evidence supporting the cavitation hypothesis of plant acoustic emissions.