Corrected infrared Sellmeier coefficients for gallium selenide

We have measured the room-temperature refractive indices of GaSe throughout the 0.7-1.4 and 2.4 - 5 μ m ranges using the minimum-deviation method of light through a prism with polarization either parallel (extraordinary refractive index n e ) or perpendicular to the crystal optical c axis (ordinary refractive index n o ). The birefringence ( Δ n ) at room temperature has been measured directly using polarized light interference fringes obtained in the transmittance from 1.73 to 4.97 μ m (three samples with thicknesses of 1108 ± 1 , 2480 ± 1 , and 2660 ± 1 μ m ) and in the range from 11.85 - 16.37 μ m (sample thickness of 6000 ± 1 μ m ). The n o , n e , and Δ n values determined from the positions of fringe maxima were compared to those obtained from prism measurements in the mid-IR and with previously published results which were mainly obtained by indirect methods. It was found that the prism method and interference fringe method resulted in values of n o , n e , and Δ n accurate to ± 0.003 and ± 0.006 , respectively.