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24 May 2018 Immersion white light scanning interferometry using elastic polymer path length compensation
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Improvements have been made to a commercial Linnik microscope in order to perform measurements in water for studying structures of transparent and non-transparent samples. One of the main goals of the present work is to study pollutants in colloidal layers immersed in liquid. The second reason to work in liquid is to increase the lateral resolution. The challenges to overcome include achieving stability in the complex Linnik design as well as the difficulty of balancing the optical distance of the two arms of the interferometer to obtain the interference fringes. The main problem is the path length compensation in the mirror arm which needs a complex mechanical design to allow a high enough number of degrees of freedom to correct alignment of the optical elements. In our system, the reference mirror arm is mounted horizontally, making liquid immersion tricky. In this work, we have investigated alternative solutions based on non-liquid elastic polymers placed between the end of the objective and the reference mirror using sodium polyacrylate (SPA) beads and PDMS (polydimethylsiloxane) slabs, with a refractive index very close to that of water. The results of the performance tests of the modified system are presented and demonstrated. The new design provides a workable system that is ready for the future study of colloidal and other samples directly in water.
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Husneni Mukhtar, Paul Montgomery, Freddy Anstotz, Rémi Barillon, and Anne Rubin "Immersion white light scanning interferometry using elastic polymer path length compensation", Proc. SPIE 10678, Optical Micro- and Nanometrology VII, 1067816 (24 May 2018);

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