Laser-induced photothermal and photovoltaic effects in an LN-based sandwich structure: competitive interplay in...

Understanding the evolution of microfluidic interfaces in light-induced multi-physical fields is of great significance for the development of lithium niobate-based microfluidic lab-on-a-chip devices. In this study, a focused laser beam is employed to simultaneously induce both photothermal and photovoltaic effects within a sandwich structure composed of an optical filter and a c-cut Fe-doped lithium niobate (LN:Fe) crystal. The coupling of thermal and electrostatic fields gives rise to the unique temporal evolution characteristics (rupture-contraction) of the microfluidic interface inside the sandwich structure, and the competitive interplay between dielectrophoretic (DEP) and thermocapillary (TEP) forces acting on the liquid film is revealed. Notably, the rupture-contraction process is found to depend on the laser illumination intensity, sandwich gap spacing, and film thickness. Based on simulations of the DEP and TEP forces exerted on the film, the increase in rupture diameter during the film rupture stage is attributed to the non-equilibrium evolution of the interface driven by a non-zero net force. In contrast, the subsequent decrease in rupture diameter during the film contraction stage is associated with the temporal variation of a quasi-static equilibrium state at the film interface. Numerical simulations of the temporal evolution of the microfluidic interface show good agreement with experimental observations.