Analyses of test glass edge-effect on coatings monitoring

During optical coatings monitoring, the test glass edgy-effect often makes the monitoring curve falseness and thin films thickness control inaccurate. The thin films edge-effect makes the films thickness different from the test glass centre to the edge, and the edge-effect gets distinctly with coating layers increasing. NBBF (narrow band pass filter) is fabricated, and its monitoring curve and spectrum curve are analyzed. The results show that the edge-effect comes from material deposition angle when test glass does not rotate, temperature and electric field different distributing on the test glass surface. Several methods are used to minish the test glass edge-effect, such as, rotating the test glass to reduce the films thickness difference caused by material deposition angle, using quartz and other glass alike material as a link between test glass and the fixture to lessen temperature and electric field different distributing, making beam size small monitor the test glass centre field, where can be considered having no thickness different. The above methods make the thickness symmetrical over the test glass, and then the experiment monitoring curve is close to the theory curve. The results are important for the thin films automatic monitoring, especially for NBBF coatings.