Object scanning scheme in wide-field low-coherence interferometry

S. Usuki; Kenjiro T. Miura

doi:10.1117/12.2320381

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18 August 2018 Object scanning scheme in wide-field low-coherence interferometry

S. Usuki, Kenjiro T. Miura

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Proceedings Volume 10749, Interferometry XIX; 1074917 (2018) https://doi.org/10.1117/12.2320381
Event: SPIE Optical Engineering + Applications, 2018, San Diego, California, United States

Abstract

The low-coherence interferometry which is usually combined with the wide-field optical microscopy is well known technique for surface profile measurement, micro step measurement and so on. One of the problems is that its axial measurement range is typically limited by its depths of field of imaging, which is determined by the numerical aperture of their objective lens and the central wavelengths of their light source. If a low-coherence interference fringe is far outside the depth of field, the measurement accuracy inevitably decreases, regardless of how well adjusted the reference mirror is. To solve this problem and improve the axial measurement range of the low-coherence interferometry in this study, an object scanning measurement scheme involving a Linnik interferometer was developed. To calibrate the system in the proposed technique, image post-processing is performed for a well-conditioned state to ensure that a lowcoherence interference fringe is generated within the depth-of-field, so that three-dimensional objects with high-aspectratio structures can be scanned along the axial direction. During object scanning, this state is always monitored and corrected by adjusting the reference mirror. By using this scheme, the axial measurement range can be significantly improved up to the working distance of the objective lens without compromising the measurement accuracy. The working distance is typically longer than 10 mm, while the depth-of-field of the microscope is generally around 0.01 mm, although it varies depending on the imaging system. In this report, the experimental setup of an object scanning low-coherence interferometry is presented, a series of experimental verifications is described, and the results are discussed.

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S. Usuki and Kenjiro T. Miura "Object scanning scheme in wide-field low-coherence interferometry", Proc. SPIE 10749, Interferometry XIX, 1074917 (18 August 2018); https://doi.org/10.1117/12.2320381

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