Refractive index of the CuAlO2 delafossite

The refractive index of the CuAlO2 delafossite has been determined from interference measurements in single crystals performed in the visible, near and mid infrared regions of the spectrum. The analysis of the refractive index dispersion corresponding to light polarization perpendicular to the c-axis (P perpendicular to c) yields a static dielectric constant of epsilon(0) = 7.7 +/- 0.8 and a low frequency electronic constant epsilon(infinity) = 5.1 +/- 0.1. The relevant infrared active E-u(up arrow) (TO) mode is found to be at 550 +/- 25 cm(-1). The electronic contribution can be well described by a Penn gap at 39 000 +/- 1000 cm(-1). Both the refractive index and its dispersion are found to be smaller for P parallel to c than for P perpendicular to c.