Optical trapping and manipulating with a transmissive and polarization-insensitive metalens

Trapping and manipulating micro-objects and high precision measurement of tiny force and displacements are of significance in physical and biological studies. Conventional optical tweezers rely on a tightly focused beam formed by a bulky microscope system. Currently, flat lenses, especially metalenses, have become emerging platforms for miniature optical tweezers application. Compared to traditional objectives, metalenses can be integrated into the sample chamber, so as to realize chip-scale light manipulation. Here, a transmissive and polarization-insensitive water-immersion metalens constructed by adaptive nano-antennas is experimentally proposed with an ultra-high numerical aperture (1.28) and a high focusing efficiency (~ 50%) at the wavelength of 532 nm. With it, a stable optical trapping has been demonstrated with the lateral trapping stiffness of more than 500 pN/(µm·W), which reaches the same order of magnitude as a conventional objective and shows better performance than other reported flat lenses. In addition, bead steering experiment exhibits lateral manipulation range more than 2 µm, including the region of approximately 0.5 µm with little changes in stiffness. We believe that this metalens enables chip-scale optical tweezers, making optical trapping and manipulating easy, reliable, high-performance and more compatible with prevalent optical tweezers applications such as single-molecule or single-cell experiments.