ABSTRACT
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Because fl atness is one of the most important parameters that characterize optical properties of optical devices such as plane mirrors and prisms, a wide variety of measuring techniques has been invented so far. The simplest method is observing the curvature of the interference fringes formed between the sample and an optical fl at. This method, however, is capable of measuring only l/20 of the curvature, and it is not always suffi cient for current applications.
