Fundamental absorption bandwidth to thickness limit for transparent homogeneous layers

The authors study how thin an absorber layer can be while still achieving a certain absorption bandwidth. Earlier work focused on metal-backed slabs; this work targets non metal-backed, transparent homogeneous layers. They derive a universal relationship between minimal layer thickness and bandwidth using the Kramers–Kronig relations. This provides fundamental limits on absorber performance beyond specific material stacks. To support the theory, they validate it with transfer matrix calculations for homogeneous materials and with full-wave numerical simulations of electromagnetic metamaterials. The authors argue these results will matter for both fundamental understanding and applied absorber design.