Uniform breaking of liquid-jets by modulated laser heating

Abstract

We report a theoretical and experimental study of the breaking of liquid jets under external periodic heating by laser pulses. In this case, jet breaking is controlled by the competition between the growth of the initial disturbances, which possess a wide wavenumber spectrum and result in the classical Rayleigh–Plateau (RP) unstable modes, and the growth of the disturbance caused by the surface tension perturbation corresponding to the periodic temperature modulation by pulsed laser heating, which appears as the thermocapillary (TC) unstable modes driven by the Marangoni flow. Our linear stability analysis shows that both the RP modes and the TC modes obey the same dispersion relation. We obtain analytical results on the range of the laser pulsing frequency that produces uniform jet breaking, at which the principal TC mode dominates the RP modes and the jet breaks at exactly the laser heating frequency, and the resulting liquid drops are uniform in size. Our theoretical prediction agrees well with experimental observations. In the uniform jet breaking range, our stability analysis also gives the growth rates of the TC modes and the jet breakup length, both of which are supported by experimental measurements. In the experiments, we also observed the growth of higher-order modes, which can again be explained quantitatively by our stability analysis.