The optical constants n and k of evaporated platinum films on glass substrates have been measured in the spectral region 4500Å–7500 Å. The reflectance Rm of gold and platinum films on a potassium tantalate (KTaO3) substrate has been measured from the substrate side and found to be somewhat lower than the calculated values. This discrepancy may be explained by relatively small alternations in n and/or k of the metal film or by scatter at the KTaO3—metal interface.
V. L. RIDEOUT and S. H. WEMPLE, "Optical Constants of Evaporated Gold and Platinum Films on Potassium Tantalate," J. Opt. Soc. Am. 56, 749-750 (1966)