26 June 2017 Topography measurements of high NA aspherical microlenses by digital holographic microscopy with spherical illumination
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In this contribution, we propose a method of digital holographic microscopy (DHM) that enables measurement of high numerical aperture spherical and aspherical microstructures of both concave and convex shapes. The proposed method utilizes reflection of the spherical illumination beam from the object surface and the interference with a spherical reference beam of the similar curvature. In this case, the NA of DHM is fully utilized for illumination and imaging of the reflected object beam. Thus, the system allows capturing the phase coming from larger areas of the quasi-spherical object and, therefore, offers possibility of high accuracy characterization of its surface even in the areas of high inclination. The proposed measurement procedure allows determining all parameters required for the accurate shape recovery: the location of the object focus point and the positions of the illumination and reference point sources. The utility of the method is demonstrated with characterization of surface of high NA focusing objects. The accuracy is firstly verified by characterization of a known reference sphere with low error of sphericity. Then, the method is applied for shape measurement of spherical and aspheric microlenses. The results provide a full-field reconstruction of high NA topography with resolution in the nanometer range. The surface sphericity is evaluated by the deviation from the best fitted sphere or asphere, and the important parameters of the measured microlens: e.g.: radius of curvature and conic constant.
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Michal Józwik, Michal Józwik, Marta Mikuła, Marta Mikuła, Tomasz Kozacki, Tomasz Kozacki, Julianna Kostencka, Julianna Kostencka, Christophe Gorecki, Christophe Gorecki, } "Topography measurements of high NA aspherical microlenses by digital holographic microscopy with spherical illumination", Proc. SPIE 10329, Optical Measurement Systems for Industrial Inspection X, 103290C (26 June 2017); doi: 10.1117/12.2270150; https://doi.org/10.1117/12.2270150

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