Invited Speakers
Plenary talks:
Ufuk Kilic:
Spectroscopic ellipsometry based optical analysis of hybrid metamaterial platforms
University of Nebraska Lincoln, USA.; The Pennsylvania State University, USA.; and Lund University, SE
} Highly uniform, spatially coherent, axially and/or radially heterogeneous, subwavelength scale structures known as metamaterials enable the extensive control of light–matter interactions at the nanoscale [1,2]. Unlike their bulk counterparts, the metamaterial systems offer strong tunability of their inherent material properties, including optical, mechanical, magnetic, and electronic, for example. However, accurate and correct optical characterization of advanced nano-manufactured metamaterial platforms is the main critical challenge in front of their use in myriad technological applications in optics and photonics. Hence, there is a need for systematic, theory-driven, application-oriented, experimental fabrication, characterization, and verification methods.In this plenary talk, I will present and discuss different metamaterial platforms which were fabricated by using the electron beam evaporated glancing angle deposition (GLAD) technique with a programmable substrate manipulator. We provide access to their optical and photonic properties by performing series of systematic and comprehensive experimental optical characterization and theoretical simulations using generalized Mueller matrix spectroscopic ellipsometry (MM-SE) and finite element modeling (FEM), respectively. For example, by operating MM-SE instrument in both straight-through transmission and near-normal reflection modes, we experimentally demonstrated that GLAD of helical and broken L-shape metamaterial platforms reveal tunable, strong, and broadband chiroptical responses [1]. The use of full-wave FEM simulations can help to not only identify and understand the resonant chiral response of the metamaterials but also visualize their enhanced chiral near-field distributions at the nanoscale, a very important property for chiral light-matter interaction applications. We will share our results on the evolution of depolarization factors in the anisotropic Bruggeman effective medium approximation for highly ordered columnar nanostructures from zirconia, silicon, titanium, and permalloy on silicon substrates with varying column lengths. We observe a material independent, i.e., universal, inverse column length dependence of the depolarization factors and the anisotropic optical properties.
As an outlook, we also plan to briefly share our recent research outputs regarding (i) the incorporation of ultra-wideband gap materials to obtain UV-active chirality response, (ii) the enhanced chirality response from topological edge states, and (iii) the nonlinear 2nd harmonic optical performances of helical nanostructures.
References
[1] Kilic, U.,et al. Advanced Functional Materials 31.20: 2010329, (2021).
[2] Kilic, U.,et al. Scientific Reports9.1: 71 (2019).
Andreas Furchner:
Infrared Ellipsometry: Recent Progress in Mueller-Matrix and Laser-Based Instrumentation
Helmholtz-Zentrum Berlin für Materialien und Energie, DE
Instrumentation - Helmholtz-Zentrum Berlin für Materialien und Energie, DE
Infrared spectroscopic ellipsometry (IR-SE) is a well-established non-destructive technique that probes the refractive and absorptive properties of thin films and surfaces with monolayer sensitivity. The IR spectral range can deliver information on chemical composition, molecular interactions, conductivity, anisotropy, as well as changes and reactions at surfaces and interfaces. We present recent instrumental developments in IR-SE that have led to significant advances of the technique with respect to broadband capabilities, temporal, spatial and spectral resolution, as well as accessible polarization properties.
The use of achromatic optical polarization elements has enabled broadband spectral studies (up to 8000–700 cm–1) for full 4 x 4 infrared Mueller-matrix ellipsometry [1–3], allowing one to probe arbitrary anisotropic and/or depolarizing thin films. Sensitivities of up to 5 · 10–5 have become possible in signal-to-noise optimized measurement configurations [3].
With the incorporation of quantum cascade lasers (QCLs) in novel IR ellipsometer designs, both spatial and temporal resolution were improved substantially [4, 5]. Laser-based infrared ellipsometry thus enables diffraction-limited hyperspectral imaging applications. On the other hand, time resolutions of about 100 ms per spectrum and 10 µs at a single wavelength open the door for exciting new in situ and operando studies in biomedical applications, surface reaction analyses and thin-film catalysis. The feasible time resolution for mid-infrared spectral measurements can be further pushed into the 10 µs range by incorporating dual-comb laser sources. Infrared dual-comb polarimetry [6] can thus probe spectrally the co- and cross-polarized amplitude and phase properties of anisotropic samples on sub-ms time scales.
Financial support by the European Union through EFRE 1.8/13 and by the Federal Ministry of Education and Research in the framework of the project CatLab (03EW0015A/B) is gratefully acknowledged.
References:
[1] E. Garcia-Caurel, A. Lizana, G. Ndong, B. Al-Bugami, C. Bernon, E. Al-Qahtani, F. Rengnez, A. de Martino, Applied Optics 2015, 54 (10), 2776–2785.
[2] A. Furchner, C. Walder, M. Zellmeier, J. Rappich, K. Hinrichs, Applied Optics 57 (2018) 7895–7904.
[3] A. Furchner, C. Kratz, W. Ogieglo, I. Pinnau, J. Rappich, K. Hinrichs, Journal of Vacuum Science & Technology B 2020, 38 (1), 014003.
[4] A. Furchner, K. Hinrichs, Advanced Optical Technologies 2022, 11 (3–4), 55–56.
[5] A. Ebner, M. Brunner, K. Hingerl, M. Brandstetter, Optics Letters 2023, 48 (9), 2293–2296.
[6] K. Hinrichs, B. Blevins, A. Furchner, N. S. Yadavalli, S. Minko, R. Horvath, M. Mangold, Natural Sciences 2023, 3 (2), e20220056.
Tatiana Novikova:Recent advances of imaging Mueller polarimetry for biomedical applications
LPICM, CNRS, Ecole polytechnique, IP Paris, Palaiseau, FR.; Department of Biomedical Engineering, Florida International University, Miami, USA.
The development of the accurate and reliable methods for tissue diagnosis is of paramount importance because an early detection and grading of any disease significantly improves patients’ perspectives to be cured and facilitate the medical treatment. The variety of optical techniques (e.g. optical coherence tomography, fluorescence spectroscopy, Raman spectroscopy, etc.) has been explored recently to assist the decision of medical doctors, but each technique has its limitations (e.g. measurement time, spatial resolution, reliability, side effects, etc.). Recently the potential of multi-spectral imaging Mueller polarimetry operating in a visible wavelength range was extensively explored and it proved to be a promising optical modality for many biomedical applications.The custom-built imaging Mueller polarimetric systems based on ferroelectric liquid crystals for the fast polarization modulation were used for the visualization and staging of cancerous lesions, digital histology, regenerative medicine, brain studies, etc. The wide-field polarimetric images of thick colon, cervical and brain specimens recorded in reflection geometry revealed high sensitivity of polarized light to structural anisotropy of tissue related to the presence of collagen fibers or bundles of neurons, as validated by histology analysis. Tissue malformations break an intrinsic optical anisotropy of healthy tissue, thus, leading to the increase of contrast between healthy and anomalous zones in the polarimetric images compared to the unpolarized intensity images. These contrasts can be used for the optical diagnosis of tissue and the delineation of pathological zones.
Our recent advances in using imaging Mueller polarimetry for medical diagnosis will be presented. Future perspectives of using this approach for biomedical applications will also be discussed
Tutorial talks:
Chris Sturm: Ellipsometry of optically anisotropic material
Felix Bloch Institute for Solid State Physics, Universität Leipzig, DE
}About 90% of all-natural crystals are optically anisotropic, i.e. the properties of an electromagnetic wave propagating inside such a material depends on the polarization as well as on the propagation direction of this wave. Furthermore, if light impinging an interface made of an optically anisotropic material, mode conversion takes place. This means that s-polarised light is partly converted into p-polarised light, or vice versa, upon reflection or transmission. Thus, standard ellipsometry, which determines the ratio of the reflection coefficients between s- and p-polarised light cannot be applied in general and generalised ellipsometry have to be used.
Here, the determination of the dielectric function of optically anisotropic material by means of generalised ellipsometry will be discussed. In contrast to optically isotropic samples, the dielectric function is not a scalar but rather a symmetric complex-valued tensor of rank two. Note, all tensor elements must fulfil the Kramers-Kronig relation to be physical meaning full. In order to gain a deeper understanding on the nature of the excitations of the dielectric function, a decomposition into its contribution is done. Here, the dielectric tensor elements cannot be treated independently of each other in general and each excitation, which contributes in the off-diagonal element, must contribute also to at least one diagonal element of the dielectric function. Two approaches are presented for such a decomposition of the dielectric function, which allows a deep understanding of the properties of each excitation, e.g., nature, orientation and magnitude.
Premysl Marsik:
Ultrathin films in infrared/THz range
University of Fribourg, CH
The optical response of a thin film on a substrate is a cornerstone topic in spectroscopic ellipsometry and is often discussed for the case of a thin film in the visible range with d≈λ. The situation is quite different for the same film, when studied with long-wavelength infrared or THz radiation. Since the wavelength exceeds by far the thickness of the film, one can speak about optically ultrathin film (d<<λ).In this tutorial, I will briefly revisit the transfer matrix formalism and introduce the ultrathin film approximation, which is instrumental in understanding the ellipsometric contrast in this scenario. In particular, I will discuss several examples of ultrathin systems in the context of our research on complex oxides grown by Pulsed Laser Deposition on crystalline substrates. Oxide substrates tend to have rather strong infrared active phonon modes, which dominate infrared response, whereas the thin film only gives rise to small modifications of the spectra. The contrast in the ellipsometric quantities is then proportional to the difference of optical conductivity between the substrate and the film but is also modulated by Brewster modes and the optically active TO and LO phonon modes of the substrate.
I will include comments on the main features of systems with multilayers, anisotropic substrate or film.
Oriol Arteaga: Challenging measurements with spectroscopic ellipsometry and polarimetry: anisotropy, optical activity, and spatial dispersion - Universitat de Barcelona, ES
Spectroscopic ellipsometry is widely recognized for its exceptional sensitivity to ultra-thin films. This sensitivity arises from the application of Fresnel equations, which can translate minuscule variations in film thickness into significant phase shifts. However, this "phase advantage" diminishes when determining the optical constants of materials affected by "bulk" optical phenomena such as anisotropy, optical activity, or spatial dispersion. While these effects are amplified in transmission configurations, they present substantial challenges in reflection setups, both in measurement and interpretation.In this presentation, we present our studies on crystalline materials that exhibit anisotropy, optical activity, and spatial dispersion. Anisotropy in crystals refers to their ability to exhibit distinct physical or optical properties along different crystallographic directions. Optical activity, observed in non-centrosymmetric crystals, involves the rotation of the polarization plane as a result of the crystal lattice's asymmetric arrangement of atoms or molecules. Spatial dispersion, on the other hand, refers to the dependency of dielectric properties on the wavevector at a constant frequency. Essentially, it implies that the electromagnetic response of a medium is influenced not only by the wavelength but also by the direction in which the wave propagates within the medium, even in materials that are expected to exhibit isotropic optical behavior based on crystal symmetry. The recent advancements made to enhance the sensitivity of our in-house Mueller matrix ellipsometers have enabled us to delve deeper into the characterization of complex materials and shed light on these optical properties. By overcoming the limitations posed by these bulk optical effects, we contribute to a more comprehensive understanding of the intricate behavior exhibited by these materials.
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