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Research on full-field measurement of optical film thickness by processing double interferometric fringes based on digital wavefront interferometry

In this paper, a novel optical-film thickness measurement method by the concurrent phase-unwrapping technology of double interferometric fringes based on digital wavefront interferometry (DWI) is presented. By using this method, some experiments were implemented on some substrates covered with a kind of optical film such as mono-layer transparent photoresist. The experimental values of photoresist-layer thickness were acquired by the computer-aid digital processing of two groups of interferometric fringes synchronously. These results match well with accurate data measured by spectroscopic ellipsometer. Compared with common techniques of optical-film thickness measurement, the proposed method has a few advantages as following: non-contact, undamaged, realtime, adaptive capacity to environment and high accuracy, etc. Theoretical simulation and experimental studies show that the method has favorable measuring robustness. In addition, the method can be applied to guide, control and improve optical fabrication based optical film techniques. Furthermore, it is also applicable to the thickness measurement of curved-surface monofilm or planar multi-layer film, which is important for the optical film-coating of conventional optical systems based on curved-surface lens.