  Enhancing the interaction strength between graphene and light is an important
objective for those seeking to make graphene a relevant material for future
optoelectronic applications. Plasmonic modes in graphene offer an additional
pathway of directing optical energy into the graphene sheet, while at the same
time displaying dramatically small optical confinement factors that make them
an interesting means of coupling light to atomic or molecular emitters. Here we
show that graphene plasmonic nanoresonators can be placed a quarter wavelength
from a reflecting surface and electronically tuned to mimic a surface with an
impedance closely matched to freespace (Z0 = 377{\Omega}). This geometry -
known in early radar applications as a Salisbury screen - allows for an order
of magnitude (from 2.3 to 24.5%) increase of the optical absorption in the
graphene and provides an efficient means of coupling to the highly confined
graphene plasmonic modes.
