  Using the non-equilibrium Keldysh formalism, we solve the equations of motion
for electron-phonon superconductivity, including an ultrafast pump field. We
present results for time-dependent photoemission spectra out of equilibrium
which probes the dynamics of the superconducting gap edge. The partial melting
of the order by the pump field leads to oscillations at twice the melted gap
frequency, a hallmark of the Higgs or amplitude mode. Thus the Higgs mode can
be directly excited through the nonlinear effects of an electromagnetic field
and detected without any additional symmetry breaking.
