  The physics of optically-induced superconductivity remains poorly understood,
with questions that range from the underlying microscopic mechanism to the
macroscopic electrical response of the non-equilibrium phase. In this paper, we
study optically-induced superconductivity in K$_{3}$C$_{60}$ thin films, which
display signatures of granularity both in the equilibrium state below T$_{c}$
and in the nonequilibrium photo-induced phase above T$_{c}$. Photo-conductive
switches are used to measure the ultrafast voltage drop across a
K$_{3}$C$_{60}$ film as a function of time after irradiation, both below and
above T$_{c}$. These measurements reveal fast changes associated with the
kinetic inductance of in-grain superconductivity, and a slower response
attributed to the Josephson dynamics at the weak links. Fits to the data yield
estimates of the in-grain photo-induced superfluid density after the drive and
the dynamics of phase slips at the weak links. This work underscores the
increasing ability to make electrical measurements at ultrafast speeds in
optically-driven quantum materials, and demonstrates a striking new platform
for optoelectronic device applications.
