Coherent perfect absorption mediated enhancement of transverse spin in a gap plasmon guide

We consider a symmetric gap plasmon guide (a folded Kretschmann configuration) supporting both symmeric and antisymmetric coupled surface plasmons. We calculate the transverse spin under illumination from both the sides like in coherent perfect absorption (CPA), whereby all the incident light can be absorbed to excite one of the modes of the structure. Significant enhancement in the transverse spin is shown to be possible when the CPA dip and the mode excitation are at the same frequency. The enhancement results from CPA-mediated total transfer of the incident light to either of the coupled modes and the associated large local fields. The transverse spin is localized in the structure since in the ambient dielectric there are only incident plane waves lacking any structure.