Terahertz refractive index matching solution.

We report on the fabrication and characterisation of a terahertz (THz) refractive index matching solution (TeraSol) based on barium titanate (BaTiO) particles and benzocyclobutene (BCB). The high refractive index of BaTiO in the THz range makes this material ideal for tuning the effective refractive index of the solution over a wide range. Exploiting the effective medium approximation, we are able to determine the concentration of BaTiO particles necessary to obtain target refractive index values between n = 1.8 and n = 5, optimised to match those of substrates widely used in the THz. TeraSol can dramatically reduce the reflections from the substrate during measurements with THz time domain spectroscopy at cryogenic and room temperature. These properties make TeraSol an appealing material for anti-reflective coatings.