Tunable Optofluidic Curvature for Micromanipulation

Manipulating micro/nanoparticles on deformed liquid interfaces induced by radiation pressure presents an active, non-invasive, and contactless method. However, a significant challenge arises due to the relatively small magnitude of the radiation force in normal incidence. Nevertheless, this technique holds immense utility in controlling particle movement at interfaces, with numerous applications in both physical and biological contexts. To overcome this, the peculiar properties of total internal reflection (TIR) in retro-reflection mode are expoited to create a approximate to 1 mu m$\approx \ 1\nobreakspace \umu m$ high amplitude bulge on the water surface, which can migrate 2 mu m$2\nobreakspace \umu m$ radius particles as forcibly as the traditional micro-post paradigm. The bulge height is measured using an interferometric technique, and the underlying physics are demonstrated using an imitated particle with a capillary charge. By shining two pump lasers, an interface shape is created with increasing complexity, and the relative pump laser intensity is tuned to migrate particles in the desired direction. The method provides a non-invasive and contactless way to remotely actuate almost all types of micro/nanoparticles at the liquid surface. To tackle insufficient radiation pressure at the liquid interface during micro-particle manipulation, total internal reflection in retro-reflection mode is used to create a 1 mu$\umu$m high water surface bulge. This bulge manipulates 2 mu$\umu$m radius particles with precise control through pump laser intensity modulation, providing a non-invasive, contactless method to manipulate various micro and nanoparticles at the liquid-air interface.image