  We report ultrafast surface pump and interface probe experiments on
photoexcited carrier transport across single crystal bismuth films on sapphire.
The film thickness is sufficient to separate carrier dynamics from lattice
heating and strain, allowing us to investigate the time-scales of momentum
relaxation, heat transfer to the lattice and electron-hole recombination. The
measured electron-hole ($e-h$) recombination time is 12--26 ps and ambipolar
diffusivity is 18--40 cm$^{2}$/s for carrier excitation up to $\sim 10^{19}
\text{cm}^{-3}$. By comparing the heating of the front and back sides of the
film, we put lower limits on the rate of heat transfer to the lattice, and by
observing the decay of the plasma at the back of the film, we estimate the
timescale of electron-hole recombination. We interpret each of these timescales
within a common framework of electron-phonon scattering and find qualitative
agreement between the various relaxation times observed. We find that the
carrier density is not determined by the $e-h$ plasma temperature after a few
picoseconds. The diffusion and recombination become nonlinear with initial
excitation $\gtrsim 10^{20} \text{cm}^{-3}$.
