| 摘要 |
An object of the present invention is to measure thickness distribution with precision by using a simple device configuration without being affected by vibrations of a to-be-measured object. In the present invention, for each of the front and the back surfaces of a to-be-measured object 1, each of light beams obtained by branching into two an emitted light beam from a laser light source 2 is further branched into two. Then, the light beams are reflected in reference surfaces and measurement points 1a and 1b mutually in a front and back relation, so that non-interference light beams Pax and Pbx each of which contains the reference light beam and the object light beam as mutually orthogonal polarization components are acquired. Then, each light beam is branched into a plurality. Onto one or more of the branched light beams, phase shift is performed in which a change is imparted to the phase difference between the orthogonal polarization components by using wavelength plates a261, a263, and a264 and the like. Then, in the branched light beams after the phase shift, common polarization components are extracted with adopting as a reference the polarization directions of the reference light beam and the object light beam so that interference light beams Qa1 to Qa4 and Qb1 to Qb4 are acquired. From their intensities, the phase difference between the polarization components of the reference light beam and the object light beam in the non-interference light beam is calculated. Then, thickness distribution in a to-be-measured object 1 is calculated from the distribution of the phase difference.
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