Planar diffractive lens design for sub-100 nm spots at vacuum ultraviolet wavelengths

Planar diffractive lenses (PDLs) based on the principle of optical superoscillation, have revolutionized far-field super-resolution imaging. A plethora of versatile PDLs have been designed for the visible wavelengths. However, it is challenging to realize PDLs in the vacuum ultraviolet (VUV) band. Here we demonstrate what we believe to be a new scheme to engineer VUV-focused PDLs possessing high transmission efficiency and sub-diffraction limit focusing, which is achieved by illuminating focused light on a self-designed multi-zone PDL. By leveraging the vector angular spectrum method and the binary particle swarm optimization algorithm, the PDL features not only a long focal length (∼56λ) and compact axial focus (∼3λ) but also generates a sub-diffraction focal spot (∼79 nm) and high transmission efficiency (∼86.5%) with a λ = 177 nm circularly polarized light illumination. Furthermore, we demonstrate how key aberrations in a refractive converging lens affect the PDL's focusing properties. In addition, we propose a characterization scheme for the PDL sub-100 nm focusing experiment in a vacuum chamber. The PDL is expected to enable miniaturization and integration of super-resolution optical systems in the VUV band.