Optical reflectance of the quasi two dimensional compound Hg₂.₈₆AsF₆ has been investigated in the optical range, 0.5 to 4 eV. The spectra clearly show a plasma edge at 3 eV. They are fitted to a Drude model and two Lorentz oscillators. From the plasma frequency and the model parameters values for the dc conductivity and the effective mass and an estimate of the crytsal anisotropy have been obtained. The results compare well with earlier electrical measurements on this compound. / Thesis / Master of Science (MSc)