  Wave absorption in time-invariant, passive thin films is fundamentally
limited by a trade-off between bandwidth and overall thickness. In this work,
we investigate the use of temporal switching to reduce signal reflections from
a thin grounded slab over broader bandwidths. We extend quasi-normal mode
theory to time switching, developing an ab initio formalism that can model a
broad class of time-switched structures. Our formalism provides optimal
switching strategies to maximize the bandwidth over which minimal reflection is
achieved, showing promising prospects for time-switched nanophotonic and
metamaterial systems to overcome the limits of time-invariant, passive
structures.
