Ptychographic imaging ellipsometry

Matthias Gouder; Menqgi Du; Stefan M. Witte

doi:10.1117/12.3022978

18 June 2024 Ptychographic imaging ellipsometry

Matthias Gouder, Menqgi Du, Stefan M. Witte

Proceedings Volume PC13023, Computational Optics 2024; PC130230B (2024) https://doi.org/10.1117/12.3022978
Event: SPIE Optical Systems Design, 2024, Strasbourg, France

Abstract

Retrieving the complex refractive index is important to infer chemical and structural properties of a specimen. Ellipsometry is the standard method to measure the refractive index. However, imaging an object with spatially varying refractive index with ellipsometry is difficult. Here, we use ptychography, which is a lensless imaging technique, to image the complex refractive indices of a multi-layer specimen. In our setup, we use a weakly focused laser beam to scan across a specimen. At each scan position, a coherent diffraction from the illuminated area on the specimen is captured with a camera. The diffraction patterns are used to reconstruct both the probe and the reflectivities of the specimen. To retrieve the refractive indices, we define a physical model that describes the reflection in the sample plane and use automatic differentiation to solve for the refractive indices. In contrast to ellipsometry, we also acquire the spatial phase change, which forms a strong constraint in the model, increasing the accuracy of the refractive index reconstructions. Finally, we provide an estimate of the uncertainty on the retrieved refractive indices using monte-carlo simulations.

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Matthias Gouder, Menqgi Du, and Stefan M. Witte "Ptychographic imaging ellipsometry", Proc. SPIE PC13023, Computational Optics 2024, PC130230B (18 June 2024); https://doi.org/10.1117/12.3022978

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KEYWORDS

Ellipsometry

Refractive index

Diffraction

Polarization

Reconstruction algorithms

Reflectivity

Simulations

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