Nanoscale precision brings experimental metalens efficiencies on par with theoretical promises

Metalenses are flat lenses, where sub-wavelength, so-called meta-atoms manipulate the electric field to perform a given lens function. Compared to traditional lenses, the two main drawbacks of metalenses are their achromatic limitations and low efficiencies. While an abundance of simulations show that efficiencies above 90% are attainable for low numerical apertures (NA), experimental reports showing such high efficiencies are limited. Here, we use electron-beam lithography (EBL) to realize a set of lenses with varying NA from 0.08 to 0.93. The low NAs were expected to fit the model, and the higher NAs determine the validity range of the model. We find that measured efficiencies above 92% for NA = 0.24 are achievable, and that a slight modification of the simulation model extends its validility to NA = 0.6. Based on our results, we discuss that the lower efficiencies reported in the literature are caused by low-fidelity manufacturing, closing the efficiency gap between measurements and simulation in metalens fabrication.