Novel methods for determining the optical constants of anisotropic polymer films: New application of prism wave-guide coupling.

摘要

A new internal reflected intensity analysis method (IRIA) for determination of the three-dimensional refractive indices and extinction coefficients of a polymer film sample, which can be both weakly and highly absorbing, was developed by this study. The IRIA method utilizes the intensity information rather than the conventional mode angle values to acquire the optical constants of a polymer film sample with a prism wave-guide coupler. Thus, the IRIA method overcomes the limitation of the present prism waveguide coupler technique that can only measure the refractive index of a weakly absorbing sample. By using a Metricon PC-2010 as the skeletal framework, a prototype modified prism wave-guide coupler instrument was developed for application of the IRIA method. A comparison study on Solvent Blue 59 dyed polystyrene spin coated films with ellipsometry, UV-VIS-NIR combined with a profilometer, and the IRIA method indicates that IRIA is a feasible method to obtain the three-dimensional refractive indices and extinction coefficients of a polymer film sample. In addition, the IRIA based modified prism wave-guide coupler was also used to study the optical properties of a conducting polymer polyaniline. Another major contribution accomplished by this research work is that an inherent deficiency in the mode equation for a prism wave-guide coupler or a leaky wave-guide was identified. A new four-wave model was proposed to replace the conventional three-wave model to resolve this deficiency. Based on the four-wave model concept, an improved mode equation for a prism wave-guide coupler or a leaky waveguide has been derived. Due to the inapplicability of the least square method, a PeakValue-Search method was developed to solve the improved mode equation. The improved mode equation based Peak-Value-Search method is able to eliminate the complication of the influence of the air gap, which has to be explicitly considered in a conventional prism wave-guide coupler technique.