Infrared optical properties of multiferroic FeTe$_{2}$O$_{5}$Br single crystal*

Reflection as a function of temperature has been measured on a single crystal of the anisotropic multiferroic FeTe$_{2}$O$_{5}$Br utilizing light spanning the far infrared to the visible portions of the electromagnetic spectrum. The complex dielectric function and optical properties along all three principal dielectric axes were obtained via Kramers-Kronig analysis and by fits to a Drude-Lorentz model. Transmission in the terahertz region as a function of temperature and magnetic field is also described, with particular focus on temperatures around the $\sim $10 K transition to the multiferroic state.