  The finite momentum optical response $\sigma({\boldsymbol{q}},\omega)$ of
graphene can be probed with the innovative technique of infrared nanoscopy
where mid-infrared radiation is confined by an atomic force microscope
cantilever tip. In contrast to conventional $q\sim 0$ optical absorption which
primarily involves Dirac fermions with momentum near the Fermi momentum, $k\sim
k_F$, for finite $q$, $\sigma({\boldsymbol{q}},\omega)$ has the potential to
provide information on many body renormalizations and collective phenomena
which have been found at small $k< k_F$ near the Dirac point in electron-doped
graphene. For electron-electron interactions, the low energy excitation
spectrum characterizing the incoherent part of the quasiparticle spectral
function of Dirac electrons with $k\sim k_F$ consists of a flat, small
amplitude background which scales with chemical potential and Fermi momentum.
However, probing of the states with $k$ near $k=0$ will reveal plasmarons, a
collective state of a charge carrier and a plasmon. These collective modes in
graphene have recently been seen in angle-resolved photoemission spectroscopy
and here we describe how they manifest in near field optics.
