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Digital holographic microscopy for sub-µm scale high aspect ratio structures in transparent materials

Besaga, V.R. and Saetchnikov, A.V. and Gerhardt, N.C. and Ostendorf, A. and Hofmann, M.R.

OPTICS AND LASERS IN ENGINEERING
Volume: 121 Pages: 441-447
DOI: 10.1016/j.optlaseng.2019.05.007
Published: 2019

Abstract
This paper discusses a digital holographic microscopy approach for comprehensive and non-destructive inspection of spatially confined structures, which are characterized by the high aspect ratio of their lateral dimensions ( ∼ 1:30) and are fabricated out of transparent materials. Two-photon polymerization is chosen as a high-resolution lithographic technology for manufacturing of corresponding structures out of positive photoresin. The proposed holographic inspection method does not require any numerical methods for aberration correction and thus demonstrates rapid phase map evaluation ( ∼ 250 ms per cycle). Applicability and performance of the method has been successfully tested on a set of samples modelled to resemble step-index structures similar to the lab-on-chip basic elements, e.g. waveguides. In terms of lateral resolution a diffraction-limited operation of the proposed imaging system is ensured while vertical accuracy of 1.61 nm has been demonstrated. © 2019 Elsevier Ltd

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