GUIDED-WAVE CHARACTERIZATION TECHNIQUES FOR THE COMPARISON OF PROPERTIES OF DIFFERENT OPTICAL COATINGS

The specific behavior of optical thin films very often leads to limitations of optical system performance. Accurate characterization techniques for evaluating film properties are necessary to understand this behavior. Characterization techniques based on the propagation of guided waves in the thickness of the films appear to be very useful. We report our particular way to determine the refractive index and the thickness of both isotropic and anisotropic thin films. Guided-waves techniques are sensitive enough to detect slight variations of thin film optical constants, so we use them to study the variations of refractive index versus temperature. From this we can obtain the thermorefractive coefficients partial derivative n/partial derivative T of our layers. Moreover, we can obtain, in some cases, the nonlinear refractive index coefficient. We also measure guided-wave attenuation and laser damage threshold with a digital imaging system. These means, dependent on guided waves, are used in combination for a comparative analysis of TiO2 and Ta2O5 layers made by different deposition techniques (conventional evaporation, ion assisted deposition and ion plating).