Mr. Tim Käseberg Profile

Tim Käseberg

at Physikalisch-Technische Bundesanstalt

SPIE Involvement:

Author

Publications (7)

Proceedings Article | 23 August 2023 Presentation

Optical measurements and numerical simulations of the Mueller matrix at silicon nanowire structures

Jana Grundmann, Tim Käseberg, Bernd Bodermann

Proceedings Volume PC12619, PC1261903 (2023) https://doi.org/10.1117/12.2673770

KEYWORDS: Nanowires, Mueller matrices, Silicon, Numerical simulations, Optical testing, Process control, Ellipsometry, Solar energy, Optics manufacturing, Maxwell equations

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Proceedings Article | 23 August 2023 Presentation

Simulating achromatic plasmonic lenses with inverted design for improved nano-optics

Tim Käseberg, Stefanie Kroker, Bernd Bodermann

Proceedings Volume PC12619, PC1261909 (2023) https://doi.org/10.1117/12.2673769

KEYWORDS: Plasmonics, Lenses, Design and modelling, Nano optics, Flat optics, Integrated optics, Fabrication, Surface plasmon polaritons, Spectroscopy, Numerical simulations

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Proceedings Article | 27 October 2021 Paper

Ellipsometric characterizations of individual nanoform structures

Tim Kaeseberg, Jana Grundmann, Sven Teichert, Matthias Wurm, Thomas Siefke, Stefanie Kroker, Bernd Bodermann

Proceedings Volume 11927, 119270O (2021) https://doi.org/10.1117/12.2616273

KEYWORDS: Ellipsometry, Polarization, Nanostructures, Cameras, Optical testing, Objectives, Imaging systems, Scanning electron microscopy, Nanolithography, Microscopes

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Proceedings Article | 12 September 2021 Presentation

Optical nanoform characterization by imaging Mueller matrix ellipsometry

Tim Käseberg, Jana Grundmann, Thomas Siefke, Stefanie Kroker, Bernd Bodermann

Proceedings Volume 11876, 118760C (2021) https://doi.org/10.1117/12.2599853

KEYWORDS: Ellipsometry, Imaging systems, Nanostructures, Inverse optics, Statistical analysis, Polarization, Microscopy, Microscopes, Silicon, Ranging

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Using conventional Mueller matrix ellipsometry, the geometries of periodic nanostructures can be easily determined if the measurement fields are not smaller than the illumination spot size. Measurements on individual nanostructures smaller than this can be accounted for by imaging ellipsometry, which allows measuring all 16 Mueller matrix elements for each pixel in the camera of the imaging system. These so-called Mueller matrix images contain additional information about the spatial distribution of the sample’s polarizing properties that are useful in the characterization of individual nanostructures. We built an imaging Mueller matrix ellipsometry system for measurements in the visible regime. Our system allows for the analysis arm, which holds the CCD camera and the polarization state analyser, to be rotated freely around the sample. By this, measurements in reflection and in transmission can be performed at arbitrary angles of incidence between 37.5° and 90°. Additionally, we implemented a reflection mode for 0° angle of incidence. Using this setup, our goal is to characterize the shape of individual nanostructures much smaller than the illumination spot using the additional information from the Mueller matrix images. Thus, we designed and fabricated a sample containing various individual nanostructures with different geometrical features. The structures are of square or circular shape, ranging in size from 5 µm to 50 nm. Additionally, the square structures feature corner rounding with different radii for a transition between circle and square. With these structures, we systematically measure the influence of the shape on the Mueller matrix elements. We also investigate in using Mueller matrix images for the characterization of subwavelength sized features significantly smaller than the resolution limit of our microscope system at about 800 nm. First results show clear distinctions between opposing edges of the nanostructures in off-diagonal Mueller matrix images.

Proceedings Article | 20 June 2021 Presentation

Applicability simulations of inverted plasmonic lenses

Tim Käseberg, Thomas Siefke, Jana Grundmann, Stefanie Kroker, Bernd Bodermann

Proceedings Volume 11783, 117830E (2021) https://doi.org/10.1117/12.2591098

KEYWORDS: Lenses, Plasmonics, Near field scanning optical microscopy, Optical microscopy, Nanostructures, Diffraction, Dielectrics, Visible radiation, Surface plasmon polaritons, Super resolution microscopy

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Proceedings Article | 1 April 2020 Presentation

Enhanced nanoform metrology by imaging Mueller matrix ellipsometry combined with plasmonic support structures (Conference Presentation)

Tim Käseberg

Proceedings Volume 11352, 113520X (2020) https://doi.org/10.1117/12.2556146

KEYWORDS: Plasmonics, Ellipsometry, Metrology, Nanostructures, Microscopes, Lens design, Polarization, Near field optics, Visible radiation, Nanotechnology

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With the persistent progress in nanotechnology the importance to accurately characterize nanoscale structures steadily increases. Optical measurement techniques have proven to be well suited for this purpose. We investigate different approaches to gain more information about nanoscale features by combining polarimetric setups with specially designed nanostructures. Our experimental setup combines a dual-rotating compensator Mueller matrix ellipsometer with an optical microscope. One arm of the ellipsometer is rigid and consists of a light source, polarization state generator, and optics to focus the light onto a sample. Samples under investigation are mounted on top of a combination of rotation and translation stages to precisely adjust them into the microscope’s focus. The other arm forms the microscope part with a long working distance objective, a polarization state analyser and a CCD camera. A large aperture rotation stage allows to rotate this arm around the sample stage. Thus, measurements in reflection and transmission under different angles of incidence can be performed. The setup measures Mueller matrices for each pixel in the obtained image. Therefore, it allows to examine the polarizing properties of the sample spatially and helps to gain further topological information. This information can be additionally enhanced by supporting nanostructures placed close to the sample to extract information from the near field. Therefore, we designed plasmonic lenses for different measurement configurations. The investigations are complemented by numerical finite element simulations. These are performed to validate the design of the nanostructures and to compare them with measured values. Up to now, we characterized the experimental setup and designed and validated the supporting nanostructures and reference structures. Future steps include extending the setup with a monochromator to ensure flexible illumination, measurement of the reference structures, and the combination of setup and plasmonic lenses to further enhance the sensitivity to subwavelength sized features.