Water-immersion supercritical metalens

Abstract

Far-field super-resolution lenses are attractive due to their great potential in the application of label-free far-field optical super-resolution. In past decades, there has been a fast development in superoscillatory optical lenses, which allows engineering of optical point-spread functions in the far-field beyond the traditional Abbe diffraction limit. With the decrease of focal spot size, the sidebands will inevitably increase, especially when the spot size is close to 0.358λ/NA, where NA is the numerical aperture. However, it is of critical importance to reduce the spot size while maintaining comparatively small sidelobes for many practical applications. Here, we demonstrate a water-immersion supercritical metalens with a high-numerical aperture of 1.15. Experimental results show the generation of a super-resolution hot spot as small as 0.33λ, which is very close to the superoscillation criterion, at a distance of 60λ from the lens. More importantly, there is no significant sideband on the focal plane, and the strength of the sidelobes near the hot spot is lower than 13.3 % of the central lobe intensity. The deep compression of hot spot and the absence of large sidelobes offer a promising way to further improve the resolution of far-field label-free super-resolution microscopy.