  We calculate the two loop hard correction to the photon self-energy in an
electron-positron plasma (EPP) for arbitrary soft momenta. This provides the
only missing ingredient to obtain the Hard Thermal Loop (HTL) effective
Lagrangian at next-to-leading order (NLO), and the full photon propagator at
the same order. This result can be easily extended to obtain the soft photon
propagator in a quark gluon plasma. We use the Keldysh representation of the
real time formalism in the massless fermion limit, and dimensional
regularization (DR) to regulate any ultraviolet (UV), infrared (IR) or
collinear divergences that appear in the intermediate steps of the calculation.
In the limit of soft photon momenta, our result is finite. It not only provides
an ${\cal O}(\alpha)$ correction to the Debye mass, but also a new non-local
structure. A consistent regularization of radial and angular integrals is
crucial to get this new structure. As an application we calculate the plasmon
dispersion relations at NLO.
