Optical propulsion and levitation of metajets

The quintessential hallmark distinguishing metasurfaces from traditional optical components is engineering materials and structures to manipulate light at will. Enabling this engineering freedom, in a reverse manner, to control the motion of objects constituted by metasurfaces could extend our capability of optical manipulation at different scales. Here, we introduce generalized optical manipulation by recapitulating metasurfaces as engineered interfaces with anomalous reflection and refraction. Upon combining Newton's law of motion and generalized Snell's law, we find that three-dimensional motions would be possible by inducing an extra wavevector component. As an example, we achieve this condition through a spatially distributed phase gradient using purposely arranged silicon nanopillars. Our experiments and simulations simultaneously reveal an in-plane propulsion and out-of-plane levitation of metasurfaces not seen in other optical manipulations. The optical force scales with incident power and is not fundamentally dependent on the size of the metajet, suggesting opportunities to scale this concept toward large-area applications such as interstellar light sails.