Polarization-encoded quadrature coherence scanning interferometry

Abstract

Coherence scanning interferometry is a non-contact optical measurement technique used for high-resolution, three-dimensional surface topography characterization. The physical principle of this technique allows to measure the shape of an object, whether its surface is smooth or rough. The measurement system is basically an interferometer with an area image sensor at the output and the object to be measured used in place of one of the mirrors. The captured interferograms represent a large amount of data, which results in long measurement times. To reduce the measurement time, we introduce a measurement method based on the use of light polarization. A λ/8 wave plate causes two interference patterns to be generated at the output of the interferometer for each pixel. Two image sensors at the output of the interferometer capture pairs of interferograms. The interferograms in the pair are mutually phase shifted by π/2. The interferogam envelope is easily calculated from the pair of interferograms. Interferograms can be acquired with high undersampling, which allows for short measurement times.