A Massively Degenerate Coherent Perfect Absorber

In the field of non-Hermitian photonics it is a well-established concept that a time-reversed laser acts as a “coherent perfect absorber” (CPA). However, CPAs are usually limited to a single, judiciously shaped wavefront (‘mode’). Here, we demonstrate how this limitation can be overcome by time-reversing a “degenerate cavity laser”, based on a cavity that self-images any incident light-field onto itself. Placing a weak, critically-coupled absorber into this cavity, ensures that any incoming wavefront is absorbed with close to perfect efficiency.