Twisting phase and intensity of light with plasmonic metasurfaces.

Twisting light in both phase and intensity has recently drawn great interests in various fields related to light-matter interactions such as optical manipulation of particles and quantum entanglement of photons. Conventionally, bulky optical components are required to produce such twisted optical beams, which significantly limits their applications in integrated photonics and optical chips. Here, we design and demonstrate aluminum plasmonic metasurfaces consisting of nanoslit antennas as ultracompact beam converters to generate the focused twisted beams in both phase and intensity across the visible wavelength range. The metasurface is encoded with the combined phase profile containing the helico-conical phase function together with a Fourier transform lens based on the Pancharatnam-Berry (PB) geometric phase. It is demonstrated that the created twisted beams simultaneously possess three-dimensional (3D) spiral intensity distribution around the propagation axis and complex phase structure containing both the central vortex and the peripheral vortex string. Moreover, the twisted beam exhibits an arithmetic intensity spiral at the focal plane with the maximum photon concentration located at the leading point of the spiral. Our results show the promising potential for advancing metasurface-based integrated devices in many applications of light-matter interactions.