Perfect Absorption at the Ultimate Thickness Limit in Planar Films

Reducing device volume is one of the key requirements for advanced nanophotonic technologies; however, this demand is often at odds with designing highly absorbing elements which usually require sizable thicknesses, such as for detector and sensor applications. Here we theoretically explore the thickness limitations of perfectly absorbing resonant systems and show surprisingly low bounds on minimal required thicknesses for total light absorption in thin planar films. We present a framework for understanding, predicting, and engineering topologically protected perfect absorption in a wide range of resonantly absorbing materials. The proposed analytical approach leads to a simple relation between a perfect absorber's thickness and dielectric function loss, which also serves as a guide for determining the absorption potential of existing and emerging materials at the ultimate thickness limit. The presented results offer new insights into the extremes of light-matter interaction and can facilitate the design of ultrasensitive light absorbers for detector and sensor systems.