A new method based on confocal microscopy is presented to measure the distance between the focus of an objective lens
and the curved surface. The focus error signal based on this method is constructed. And this signal features not only the
possession of the linear relationship to the defocus, that is the distance between the focus of the objective lens and the
curved surface, and direction information of defocus and a wide measuring range, but also the independence of the tilt
angle of curved surface, the power fluctuation and the like.
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.
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