Obtaining Accurate Reflectance and Transmittance Measurements for optical Coatings

摘要

The accuracy of the derivation of index of refraction values, n and k, for optical thin film coating materials depends heavily on the accuracy of the spectrophotometric measurement data supporting the derivation. Any reflectance and/or transmittance errors will lead to errors in the resulting n- and k-values, which will in turn cause errors in the associated designs, and the actual coatings will have errors and depart from that which was intended. These derivations are an important part of the production of optical thin films, and need to be fully understood and carefully exercised. Possible causes of measurement errors, calibration procedures, and working standards are discussed. Tests for photometric accuracy and linearity are suggested. Techniques for calibrating spectrophotometers and obtaining accurate reflectance and transmittance data are reviewed.