  The in-plane complex optical properties of the iron-chalcogenide
superconductor FeTe0.55Se0.45 have been determined above and below the critical
temperature Tc = 14 K. At room temperature the conductivity is described by a
weakly-interacting Fermi liquid; however, below 100 K the scattering rate
develops a frequency dependence in the terahertz region, signaling the
increasingly correlated nature of this material. We estimate the dc
conductivity just above Tc to be sigma_dc ~ 3500 Ohm-1cm-1 and the superfluid
density rho_s0 ~ 9 x 10^6 cm-2, which places this material close to the scaling
line rho_s0/8 ~ 8.1 sigma_dc Tc for a BCS dirty-limit superconductor. Below Tc
the optical conductivity reveals two gap features at Delta_1,2 ~ 2.5 and ~ 5.1
meV.
