Refractive indices of Sn2P2S6 at visible and infrared wavelengths.

We report on the refractive indices of Sn2P2S6 crystals in the wavelength range 550 - 2300 nm. The measurements are performed at room temperature using the minimum deviation method. The dispersion is described by a two oscillator model yielding the oscillator energies and strengths (Sellmeier parameters) for all polarization directions. The rotation of the indicatrix in the mirror plane and the direction of the optical axes have also been determined in the wavelength range lambda= 550-2200 nm.