Proceedings of the
9th International Conference of Asian Society for Precision Engineering and Nanotechnology (ASPEN2022)
15 – 18 November 2022, Singapore

Study of Two-photon Lithography using Optical Diffraction Tomography

Qi Shao1, Yanping He2, Renjie Zhou2,a and Shih-chi Chen1,b

1Department of Mechanical and Automation Engineering, The Chinese University of Hong Kong, Shatin, New Territories, Hong Kong, China

2Department of Biomedical Engineering, The Chinese University of Hong Kong, Shatin, New Territories, Hong Kong SAR, China


Two-photon photopolymerization (TPP) has recently become a popular method for fabricating 3D micro- and nanostructures. However. the reproduction fidelity of the designed micro-nanostructures is often influenced by experimental writing conditions, including laser power, exposure time, etc. To determine the appropriate writing parameters, in situ characterization of morphological features and surface roughness is needed. Traditional characterization methods for TPP, e.g., scanning electron microscopy and atomic force microscopy, have limited speed and cannot study internal structures without invasive approaches. Optical diffraction tomography (ODT) is an emerging label-free 3D imaging technique based on reconstructing the object's 3D refractive index (RI) distribution with diffraction-limited resolution. Here, we propose a non-invasive solution to fully characterize the TPP-fabricated structures using a high-speed ODT technique, which can eliminate the need for complex sample preparation, such as fluorescence labelling or metal-coating, and achieve a full 3D measurement time within 6 ms. By visualizing and studying different TPP-fabricated structures, including embedded spirals and cubes, via the ODT system, the fabrication quality, including 3D morphological features, exposure levels, and surface roughness, can be examined quantitatively. The results suggest our method can effectively improve the fabrication quality and reproducibility of TPP, generating impact to the nanofabrication community.

Keywords: 3D Printing, Two-Photon Polymerization, High-Speed Characterization, Optical Diffraction Tomography.

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