This paper presents a special configuration of white-light scanning interferometer, in which the measured gap is not located in any interference arm of the interferometer, but acts as an amplitude-and-phase modulator of the light source. Compared to the common white-light interferometer, the approach avoids the influence of the chromatic dispersion of the planar plates on the gap thickness measurement. It possesses a large measurement range of from several hundreds of nanometers to tens of microns as well as a high resolution of 0.1 nm, but does not employ any expensive equipment like spectrometer or monochromator. These advantages make our approach quite competent for the practical applications.
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