  Epitaxial bilayer films of Bi(110) and Ni host a time-reversal symmetry (TRS)
breaking superconducting order with an unexpectedly high transition temperature
$T_c = 4.1$ K. Using time-domain THz spectroscopy, we measure the low energy
electrodynamic response of a Bi/Ni bilayer thin film from $0.2$ THz to $2$ THz
as a function of temperature and magnetic field. We analyze the data in the
context of a BCS-like superconductor with a finite normal-state scattering
rate. In zero magnetic field, all states in the film become fully gapped,
providing important constraints into possible pairing symmetries. Our data
appears to rule out the odd-frequency pairing that is natural for many
ferromagnetic-superconductor interfaces. By analyzing the magnetic
field-dependent response in terms of a pair-breaking parameter, we determine
that superconductivity develops over the entire bilayer sample which may point
to the $p$-wave like nature of unconventional superconductivity.
