Thank you for visiting nature.com. You are using a browser version with limited support for CSS. To obtain
the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in
Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles
and JavaScript.
We posit that inconsistent interpretations of experimental data have led to inaccurate claims on metalens focusing efficiencies. By performing a meta-analysis, we show that extraordinary claims of high focusing efficiency at high numerical apertures are, unfortunately, not yet backed by rigorous simulation or experimental results.
In recent decades, progress in developing better nonlinear materials has not been as rapid as wished. Here I propose that this may be explained by considering the simple view of nonlinear optical phenomena as being determined mostly by the length of interaction time between photons and matter. Tentative routes towards improvements in the efficiency of nonlinear optical phenomena are suggested.
